The task seems trivial at first glance: Develop a system that automagically identifies the timezone of odyssey's current position and changes the timezone as soon as a timezone-border is crossed accordingly.

It proved to be a bit more difficult, since time borders are not systematic, but chaotic, following political (national) borders, making a simple mapping almost impossible or at least very costly in terms of performance and maintenance (time borders and DST usage change often).

Apollo-NG Time is always GPS disciplined UTC, local time is adjusted by referencing UTC as default system time and applying the correct timezone with accurate DST adjustments to the system. This way, even international-date-border crossings in either direction won't affect the system.

The simplest method found, was introduced by anselm@hook.org: Mapping timezones to colors and pixels to coordinates using a map image (6MB TIFF):

// A utility to take a longitude latitude and return a time zone in olson posix string format
// by anselm@hook.org
// this was based on data from
// http://koordinates.com/layer/751-world-time-zones/
// which was loaded into mapserver and each layer rendered as a unique color to a large image
// this code looks up that color on the map and then returns the appropriate indexed string
// see also
// http://books.google.ca/books?id=tZ2rExM1hy8C&pg=PA136&lpg=PA136&dq=blue+marble+projection&source=bl &ots=46IcxdmJar&sig=sOwzkup4vASHQSADNIQgq35BpIs&hl=en&e
i=iN8SSo-pO5iG8gT9qsCBBA&sa=X&oi=book_result&c t=result&resnum=6

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <math.h>
#include "timezones.h"

#define CONVERTNAME "convert"
#define CONVERTPATH "/usr/local/src/ImageMagick-6.7.1-0/utilities/convert"
#define INCANTATION_BUFFER_SIZE 999

int main(int argc,char **argv) {
  if(argc <3 ) {
   printf("Usage: %s longitude latitude\n",argv[0]);
   return(0);
  }
  char incantation[INCANTATION_BUFFER_SIZE];
  int timezones_length = sizeof(timezones)/sizeof(timezones[0]);
  int zonecode = 0;
  // get user supplied location
  double lon = atof(argv[1]);
  double lat = atof(argv[2]);
  // convert to equidistant projection
  int x = 2048.0f/360.0f*(180.0f+lon);
  int y = 1024.0f/180.0f*(90.0f-lat);
  int r,g,b;
  printf("Given longitude,latitude %lf,%lf\n",lon,lat);
  printf("Given pixel location x,y epsg:4326 projection at %d,%d\n",x,y);
  snprintf(incantation,
           INCANTATION_BUFFER_SIZE,
           "/usr/local/src/ImageMagick-6.7.1-0/utilities/convert timezone.tiff -format \"%%[pixel:u.p{%d,%d}]\" info:",x,y);
  printf("ImageMagic incantation is %s\n",incantation);
  FILE* f = popen(incantation,"r");
  while( fgets(incantation,INCANTATION_BUFFER_SIZE,f))
  printf("%s",incantation);
  fclose(f);
  sscanf(incantation,"rgb(%d,%d,%d)",&r,&g,&b);
  printf("Got colors %d,%d,%d\n",r,g,b );
  zonecode = ((r&248)<<1)+((g>>4)&15);
  if(zonecode > timezones_length) {
    printf("Illegal color in the image; doesn't seem to map with our range! %d\n", zonecode );
  } else {
    printf("The longitude latitude of %f,%f is in timezone %s\n",lon,lat,timezones[zonecode]);
  }
}

###################################################################

timezones.h

char* timezones[] = {
"Africa/Abidjan",
"Africa/Accra",
"Africa/Addis_Ababa",
"Africa/Algiers",
"Africa/Asmara",
"Africa/Bamako",
"Africa/Bangui",
"Africa/Banjul",
"Africa/Bissau",
"Africa/Blantyre",
"Africa/Brazzaville",
"Africa/Bujumbura",
"Africa/Cairo",
"Africa/Casablanca",
"Africa/Conakry",
"Africa/Dakar",
"Africa/Dar_es_Salaam",
"Africa/Djibouti",
"Africa/Douala",
"Africa/El_Aaiun",
"Africa/Freetown",
"Africa/Gaborone",
"Africa/Harare",
"Africa/Johannesburg",
"Africa/Kampala",
"Africa/Khartoum",
"Africa/Kigali",
"Africa/Kinshasa",
"Africa/Lagos",
"Africa/Libreville",
"Africa/Lome",
"Africa/Luanda",
"Africa/Lubumbashi",
"Africa/Lusaka",
"Africa/Malabo",
"Africa/Maputo",
"Africa/Maseru",
"Africa/Mbabane",
"Africa/Mogadishu",
"Africa/Monrovia",
"Africa/Nairobi",
"Africa/Ndjamena",
"Africa/Niamey",
"Africa/Nouakchott",
"Africa/Ouagadougou",
"Africa/Porto-Novo",
"Africa/Sao_Tome",
"Africa/Tripoli",
"Africa/Tunis",
"Africa/Windhoek",
"America/Adak",
"America/Anguilla",
"America/Antigua",
"America/Araguaina",
"America/Argentina/Buenos_Aires",
"America/Argentina/Catamarca",
"America/Argentina/Cordoba",
"America/Argentina/Jujuy",
"America/Argentina/La_Rioja",
"America/Argentina/Mendoza",
"America/Argentina/Rio_Gallegos",
"America/Argentina/San_Juan",
"America/Argentina/San_Luis",
"America/Argentina/Tucuman",
"America/Argentina/Ushuaia",
"America/Aruba",
"America/Asuncion",
"America/Atikokan",
"America/Bahia",
"America/Barbados",
"America/Belem",
"America/Belize",
"America/Blanc-Sablon",
"America/Boa_Vista",
"America/Bogota",
"America/Boise",
"America/Cambridge_Bay",
"America/Campo_Grande",
"America/Cancun",
"America/Caracas",
"America/Cayenne",
"America/Cayman",
"America/Chicago",
"America/Chihuahua",
"America/Coral_Harbour",
"America/Costa_Rica",
"America/Cuiaba",
"America/Curacao",
"America/Dawson",
"America/Dawson_Creek",
"America/Denver",
"America/Dominica",
"America/Edmonton",
"America/Eirunepe",
"America/El_Salvador",
"America/Fortaleza",
"America/Glace_Bay",
"America/Goose_Bay",
"America/Grand_Turk",
"America/Grenada",
"America/Guadeloupe",
"America/Guatemala",
"America/Guayaquil",
"America/Guyana",
"America/Halifax",
"America/Havana",
"America/Hermosillo",
"America/Indiana/Indianapolis",
"America/Indiana/Knox",
"America/Indiana/Marengo",
"America/Indiana/Petersburg",
"America/Indiana/Vevay",
"America/Indiana/Vincennes",
"America/Indiana/Winamac",
"America/Inuvik",
"America/Iqaluit",
"America/Jamaica",
"America/Juneau",
"America/Kentucky/Louisville",
"America/Kentucky/Monticello",
"America/La_Paz",
"America/Lima",
"America/Los_Angeles",
"America/Maceio",
"America/Managua",
"America/Manaus",
"America/Marigot",
"America/Martinique",
"America/Mazatlan",
"America/Menominee",
"America/Merida",
"America/Mexico_City",
"America/Miquelon",
"America/Moncton",
"America/Monterrey",
"America/Montevideo",
"America/Montreal",
"America/Montserrat",
"America/Nassau",
"America/New_York",
"America/Nipigon",
"America/Noronha",
"America/North_Dakota/Center",
"America/North_Dakota/Salem",
"America/Panama",
"America/Pangnirtung",
"America/Paramaribo",
"America/Phoenix",
"America/Port-au-Prince",
"America/Port_of_Spain",
"America/Porto_Velho",
"America/Puerto_Rico",
"America/Rainy_River",
"America/Rankin_Inlet",
"America/Recife",
"America/Regina",
"America/Resolute",
"America/Rio_Branco",
"America/Santarem",
"America/Santiago",
"America/Santo_Domingo",
"America/Sao_Paulo",
"America/St_Barthelemy",
"America/St_Johns",
"America/St_Kitts",
"America/St_Lucia",
"America/St_Thomas",
"America/St_Vincent",
"America/Tegucigalpa",
"America/Thunder_Bay",
"America/Tijuana",
"America/Toronto",
"America/Tortola",
"America/Vancouver",
"America/Whitehorse",
"America/Winnipeg",
"America/Yellowknife",
"Ameriica/Swift_Current",
"Arctic/Longyearbyen",
"Asia/Aden",
"Asia/Almaty",
"Asia/Amman",
"Asia/Anadyr",
"Asia/Aqtau",
"Asia/Aqtobe",
"Asia/Ashgabat",
"Asia/Baghdad",
"Asia/Bahrain",
"Asia/Baku",
"Asia/Bangkok",
"Asia/Beirut",
"Asia/Bishkek",
"Asia/Brunei",
"Asia/Choibalsan",
"Asia/Chongqing",
"Asia/Colombo",
"Asia/Damascus",
"Asia/Dhaka",
"Asia/Dili",
"Asia/Dubai",
"Asia/Dushanbe",
"Asia/Gaza",
"Asia/Harbin",
"Asia/Ho_Chi_Minh",
"Asia/Hong_Kong",
"Asia/Hovd",
"Asia/Irkutsk",
"Asia/Jakarta",
"Asia/Jayapura",
"Asia/Jerusalem",
"Asia/Kabul",
"Asia/Kamchatka",
"Asia/Karachi",
"Asia/Kashgar",
"Asia/Katmandu",
"Asia/Kolkata",
"Asia/Krasnoyarsk",
"Asia/Kuala_Lumpur",
"Asia/Kuching",
"Asia/Kuwait",
"Asia/Macau",
"Asia/Magadan",
"Asia/Makassar",
"Asia/Manila",
"Asia/Muscat",
"Asia/Nicosia",
"Asia/Novosibirsk",
"Asia/Omsk",
"Asia/Oral",
"Asia/Phnom_Penh",
"Asia/Pontianak",
"Asia/Pyongyang",
"Asia/Qatar",
"Asia/Qyzylorda",
"Asia/Rangoon",
"Asia/Riyadh",
"Asia/Sakhalin",
"Asia/Samarkand",
"Asia/Seoul",
"Asia/Shanghai",
"Asia/Singapore",
"Asia/Taipei",
"Asia/Tashkent",
"Asia/Tbilisi",
"Asia/Tehran",
"Asia/Thimphu",
"Asia/Tokyo",
"Asia/Ulaanbaatar",
"Asia/Urumqi",
"Asia/Vientiane",
"Asia/Vladivostok",
"Asia/Yakutsk",
"Asia/Yekaterinburg",
"Asia/Yerevan",
"Atlantic/Azores",
"Atlantic/Bermuda",
"Atlantic/Canary",
"Atlantic/Cape_Verde",
"Atlantic/Faroe",
"Atlantic/Madeira",
"Atlantic/Reykjavik",
"Atlantic/South_Georgia",
"Atlantic/St_Helena",
"Atlantic/Stanley",
"Australia/Adelaide",
"Australia/Brisbane",
"Australia/Broken_Hill",
"Australia/Currie",
"Australia/Darwin",
"Australia/Eucla",
"Australia/Hobart",
"Australia/Lindeman",
"Australia/Lord_Howe",
"Australia/Melbourne",
"Australia/Perth",
"Australia/Sydney",
"Europe/Amsterdam",
"Europe/Andorra",
"Europe/Athens",
"Europe/Belgrade",
"Europe/Berlin",
"Europe/Bratislava",
"Europe/Brussels",
"Europe/Bucharest",
"Europe/Budapest",
"Europe/Chisinau",
"Europe/Copenhagen",
"Europe/Dublin",
"Europe/Gibraltar",
"Europe/Guernsey",
"Europe/Helsinki",
"Europe/Isle_of_Man",
"Europe/Istanbul",
"Europe/Jersey",
"Europe/Kaliningrad",
"Europe/Kiev",
"Europe/Lisbon",
"Europe/Ljubljana",
"Europe/London",
"Europe/Luxembourg",
"Europe/Madrid",
"Europe/Malta",
"Europe/Marienhamn",
"Europe/Minsk",
"Europe/Monaco",
"Europe/Moscow",
"Europe/Oslo",
"Europe/Paris",
"Europe/Podgorica",
"Europe/Prague",
"Europe/Riga",
"Europe/Rome",
"Europe/Samara",
"Europe/San_Marino",
"Europe/Sarajevo",
"Europe/Simferopol",
"Europe/Skopje",
"Europe/Sofia",
"Europe/Stockholm",
"Europe/Tallinn",
"Europe/Tirane",
"Europe/Uzhgorod",
"Europe/Vaduz",
"Europe/Vatican",
"Europe/Vienna",
"Europe/Vilnius",
"Europe/Volgograd",
"Europe/Warsaw",
"Europe/Zagreb",
"Europe/Zaporozhye",
"Europe/Zurich",
"Indian/Antananarivo",
"Indian/Chagos",
"Indian/Christmas",
"Indian/Cocos",
"Indian/Comoro",
"Indian/Kerguelen",
"Indian/Mahe",
"Indian/Maldives",
"Indian/Mauritius",
"Indian/Mayotte",
"Indian/Reunion",
"Pacific/Apia",
"Pacific/Auckland",
"Pacific/Chatham",
"Pacific/Easter",
"Pacific/Efate",
"Pacific/Enderbury",
"Pacific/Fakaofo",
"Pacific/Fiji",
"Pacific/Funafuti",
"Pacific/Galapagos",
"Pacific/Gambier",
"Pacific/Guadalcanal",
"Pacific/Guam",
"Pacific/Honolulu",
"Pacific/Johnston",
"Pacific/Kiritimati",
"Pacific/Kosrae",
"Pacific/Kwajalein",
"Pacific/Majuro",
"Pacific/Marquesas",
"Pacific/Midway",
"Pacific/Nauru",
"Pacific/Niue",
"Pacific/Norfolk",
"Pacific/Noumea",
"Pacific/Pago_Pago",
"Pacific/Palau",
"Pacific/Pitcairn",
"Pacific/Ponape",
"Pacific/Port_Moresby",
"Pacific/Rarotonga",
"Pacific/Saipan",
"Pacific/Tahiti",
"Pacific/Tarawa",
"Pacific/Tongatapu",
"Pacific/Truk",
"Pacific/Wake",
"Pacific/Wallis",
"none",
"uninhabited",
""
};

Execution time: 0m3.846s

Having to have to maintain a binary for embedded systems seemed cumbersome and imagemagick is - although glorious - not really something for embedded systems. Python however is the default script language on all gentoo systems and therefore automatically available on all hosts.

The following python script only needs PIL (Python Imaging Library) which is much leaner and returns results faster with less system impact. The 6Mb TIFF File was converted to a PNG (see/download map image above) using gimp, default settings, no tags, compression 9. It's almost twice as fast but consumes only a quarter of the C memory footprint:

#!/usr/bin/python
# -*- coding: utf-8 -*-

# Deps: PIL (Python Image Library)

import os, sys
import Image

timezones = [ 
"Africa/Abidjan",
"Africa/Accra",
"Africa/Addis_Ababa",
"Africa/Algiers",
"Africa/Asmara",
"Africa/Bamako",
"Africa/Bangui",
"Africa/Banjul",
"Africa/Bissau",
"Africa/Blantyre",
"Africa/Brazzaville",
"Africa/Bujumbura",
"Africa/Cairo",
"Africa/Casablanca",
"Africa/Conakry",
"Africa/Dakar",
"Africa/Dar_es_Salaam",
"Africa/Djibouti",
"Africa/Douala",
"Africa/El_Aaiun",
"Africa/Freetown",
"Africa/Gaborone",
"Africa/Harare",
"Africa/Johannesburg",
"Africa/Kampala",
"Africa/Khartoum",
"Africa/Kigali",
"Africa/Kinshasa",
"Africa/Lagos",
"Africa/Libreville",
"Africa/Lome",
"Africa/Luanda",
"Africa/Lubumbashi",
"Africa/Lusaka",
"Africa/Malabo",
"Africa/Maputo",
"Africa/Maseru",
"Africa/Mbabane",
"Africa/Mogadishu",
"Africa/Monrovia",
"Africa/Nairobi",
"Africa/Ndjamena",
"Africa/Niamey",
"Africa/Nouakchott",
"Africa/Ouagadougou",
"Africa/Porto-Novo",
"Africa/Sao_Tome",
"Africa/Tripoli",
"Africa/Tunis",
"Africa/Windhoek",
"America/Adak",
"America/Anguilla",
"America/Antigua",
"America/Araguaina",
"America/Argentina/Buenos_Aires",
"America/Argentina/Catamarca",
"America/Argentina/Cordoba",
"America/Argentina/Jujuy",
"America/Argentina/La_Rioja",
"America/Argentina/Mendoza",
"America/Argentina/Rio_Gallegos",
"America/Argentina/San_Juan",
"America/Argentina/San_Luis",
"America/Argentina/Tucuman",
"America/Argentina/Ushuaia",
"America/Aruba",
"America/Asuncion",
"America/Atikokan",
"America/Bahia",
"America/Barbados",
"America/Belem",
"America/Belize",
"America/Blanc-Sablon",
"America/Boa_Vista",
"America/Bogota",
"America/Boise",
"America/Cambridge_Bay",
"America/Campo_Grande",
"America/Cancun",
"America/Caracas",
"America/Cayenne",
"America/Cayman",
"America/Chicago",
"America/Chihuahua",
"America/Coral_Harbour",
"America/Costa_Rica",
"America/Cuiaba",
"America/Curacao",
"America/Dawson",
"America/Dawson_Creek",
"America/Denver",
"America/Dominica",
"America/Edmonton",
"America/Eirunepe",
"America/El_Salvador",
"America/Fortaleza",
"America/Glace_Bay",
"America/Goose_Bay",
"America/Grand_Turk",
"America/Grenada",
"America/Guadeloupe",
"America/Guatemala",
"America/Guayaquil",
"America/Guyana",
"America/Halifax",
"America/Havana",
"America/Hermosillo",
"America/Indiana/Indianapolis",
"America/Indiana/Knox",
"America/Indiana/Marengo",
"America/Indiana/Petersburg",
"America/Indiana/Vevay",
"America/Indiana/Vincennes",
"America/Indiana/Winamac",
"America/Inuvik",
"America/Iqaluit",
"America/Jamaica",
"America/Juneau",
"America/Kentucky/Louisville",
"America/Kentucky/Monticello",
"America/La_Paz",
"America/Lima",
"America/Los_Angeles",
"America/Maceio",
"America/Managua",
"America/Manaus",
"America/Marigot",
"America/Martinique",
"America/Mazatlan",
"America/Menominee",
"America/Merida",
"America/Mexico_City",
"America/Miquelon",
"America/Moncton",
"America/Monterrey",
"America/Montevideo",
"America/Montreal",
"America/Montserrat",
"America/Nassau",
"America/New_York",
"America/Nipigon",
"America/Noronha",
"America/North_Dakota/Center",
"America/North_Dakota/Salem",
"America/Panama",
"America/Pangnirtung",
"America/Paramaribo",
"America/Phoenix",
"America/Port-au-Prince",
"America/Port_of_Spain",
"America/Porto_Velho",
"America/Puerto_Rico",
"America/Rainy_River",
"America/Rankin_Inlet",
"America/Recife",
"America/Regina",
"America/Resolute",
"America/Rio_Branco",
"America/Santarem",
"America/Santiago",
"America/Santo_Domingo",
"America/Sao_Paulo",
"America/St_Barthelemy",
"America/St_Johns",
"America/St_Kitts",
"America/St_Lucia",
"America/St_Thomas",
"America/St_Vincent",
"America/Tegucigalpa",
"America/Thunder_Bay",
"America/Tijuana",
"America/Toronto",
"America/Tortola",
"America/Vancouver",
"America/Whitehorse",
"America/Winnipeg",
"America/Yellowknife",
"Ameriica/Swift_Current",
"Arctic/Longyearbyen",
"Asia/Aden",
"Asia/Almaty",
"Asia/Amman",
"Asia/Anadyr",
"Asia/Aqtau",
"Asia/Aqtobe",
"Asia/Ashgabat",
"Asia/Baghdad",
"Asia/Bahrain",
"Asia/Baku",
"Asia/Bangkok",
"Asia/Beirut",
"Asia/Bishkek",
"Asia/Brunei",
"Asia/Choibalsan",
"Asia/Chongqing",
"Asia/Colombo",
"Asia/Damascus",
"Asia/Dhaka",
"Asia/Dili",
"Asia/Dubai",
"Asia/Dushanbe",
"Asia/Gaza",
"Asia/Harbin",
"Asia/Ho_Chi_Minh",
"Asia/Hong_Kong",
"Asia/Hovd",
"Asia/Irkutsk",
"Asia/Jakarta",
"Asia/Jayapura",
"Asia/Jerusalem",
"Asia/Kabul",
"Asia/Kamchatka",
"Asia/Karachi",
"Asia/Kashgar",
"Asia/Katmandu",
"Asia/Kolkata",
"Asia/Krasnoyarsk",
"Asia/Kuala_Lumpur",
"Asia/Kuching",
"Asia/Kuwait",
"Asia/Macau",
"Asia/Magadan",
"Asia/Makassar",
"Asia/Manila",
"Asia/Muscat",
"Asia/Nicosia",
"Asia/Novosibirsk",
"Asia/Omsk",
"Asia/Oral",
"Asia/Phnom_Penh",
"Asia/Pontianak",
"Asia/Pyongyang",
"Asia/Qatar",
"Asia/Qyzylorda",
"Asia/Rangoon",
"Asia/Riyadh",
"Asia/Sakhalin",
"Asia/Samarkand",
"Asia/Seoul",
"Asia/Shanghai",
"Asia/Singapore",
"Asia/Taipei",
"Asia/Tashkent",
"Asia/Tbilisi",
"Asia/Tehran",
"Asia/Thimphu",
"Asia/Tokyo",
"Asia/Ulaanbaatar",
"Asia/Urumqi",
"Asia/Vientiane",
"Asia/Vladivostok",
"Asia/Yakutsk",
"Asia/Yekaterinburg",
"Asia/Yerevan",
"Atlantic/Azores",
"Atlantic/Bermuda",
"Atlantic/Canary",
"Atlantic/Cape_Verde",
"Atlantic/Faroe",
"Atlantic/Madeira",
"Atlantic/Reykjavik",
"Atlantic/South_Georgia",
"Atlantic/St_Helena",
"Atlantic/Stanley",
"Australia/Adelaide",
"Australia/Brisbane",
"Australia/Broken_Hill",
"Australia/Currie",
"Australia/Darwin",
"Australia/Eucla",
"Australia/Hobart",
"Australia/Lindeman",
"Australia/Lord_Howe",
"Australia/Melbourne",
"Australia/Perth",
"Australia/Sydney",
"Europe/Amsterdam",
"Europe/Andorra",
"Europe/Athens",
"Europe/Belgrade",
"Europe/Berlin",
"Europe/Bratislava",
"Europe/Brussels",
"Europe/Bucharest",
"Europe/Budapest",
"Europe/Chisinau",
"Europe/Copenhagen",
"Europe/Dublin",
"Europe/Gibraltar",
"Europe/Guernsey",
"Europe/Helsinki",
"Europe/Isle_of_Man",
"Europe/Istanbul",
"Europe/Jersey",
"Europe/Kaliningrad",
"Europe/Kiev",
"Europe/Lisbon",
"Europe/Ljubljana",
"Europe/London",
"Europe/Luxembourg",
"Europe/Madrid",
"Europe/Malta",
"Europe/Marienhamn",
"Europe/Minsk",
"Europe/Monaco",
"Europe/Moscow",
"Europe/Oslo",
"Europe/Paris",
"Europe/Podgorica",
"Europe/Prague",
"Europe/Riga",
"Europe/Rome",
"Europe/Samara",
"Europe/San_Marino",
"Europe/Sarajevo",
"Europe/Simferopol",
"Europe/Skopje",
"Europe/Sofia",
"Europe/Stockholm",
"Europe/Tallinn",
"Europe/Tirane",
"Europe/Uzhgorod",
"Europe/Vaduz",
"Europe/Vatican",
"Europe/Vienna",
"Europe/Vilnius",
"Europe/Volgograd",
"Europe/Warsaw",
"Europe/Zagreb",
"Europe/Zaporozhye",
"Europe/Zurich",
"Indian/Antananarivo",
"Indian/Chagos",
"Indian/Christmas",
"Indian/Cocos",
"Indian/Comoro",
"Indian/Kerguelen",
"Indian/Mahe",
"Indian/Maldives",
"Indian/Mauritius",
"Indian/Mayotte",
"Indian/Reunion",
"Pacific/Apia",
"Pacific/Auckland",
"Pacific/Chatham",
"Pacific/Easter",
"Pacific/Efate",
"Pacific/Enderbury",
"Pacific/Fakaofo",
"Pacific/Fiji",
"Pacific/Funafuti",
"Pacific/Galapagos",
"Pacific/Gambier",
"Pacific/Guadalcanal",
"Pacific/Guam",
"Pacific/Honolulu",
"Pacific/Johnston",
"Pacific/Kiritimati",
"Pacific/Kosrae",
"Pacific/Kwajalein",
"Pacific/Majuro",
"Pacific/Marquesas",
"Pacific/Midway",
"Pacific/Nauru",
"Pacific/Niue",
"Pacific/Norfolk",
"Pacific/Noumea",
"Pacific/Pago_Pago",
"Pacific/Palau",
"Pacific/Pitcairn",
"Pacific/Ponape",
"Pacific/Port_Moresby",
"Pacific/Rarotonga",
"Pacific/Saipan",
"Pacific/Tahiti",
"Pacific/Tarawa",
"Pacific/Tongatapu",
"Pacific/Truk",
"Pacific/Wake",
"Pacific/Wallis",
"None",
"Uninhabited",
""]

lat       = float        (sys.argv[1])
lon       = float        (sys.argv[2])

# convert to equidistant pixel projection ################

x         =               2048.0/360.0*(180.0+lon)
y         =               1024.0/180.0*(90.0-lat)

tz_map    = Image.open   ("timezones.png")
tz_pix    = tz_map.load  ()

r,g,b     =               tz_pix[x,y]  # top left corner
tz_code   =               ((r&248)<<1)+((g>>4)&15)

if                       tz_code > len(timezones): 
    print "Illegal color in the image; doesn't seem to map with our range! %d" % tz_code
else: 
    print "Current position is in timezone %s" % (timezones[tz_code])

Execution time: 0m1.824s

If you can find an easier and reliable way with even less impact, don't hesitate to submit your solution to be published here as well.