В файл, где происходит работа с функциями времени добавляется строка

date_default_timezone_set("Europe/Moscow");

Строка "Europe/Moscow" в данном случае указывает часовой пос, в котором находиться сервер. Полный перечень возможных значений смотрите ниже

Africa 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/Ceuta, Africa/Conakry, Africa/Dakar, Africa/Dar_es_Salaam, Africa/Djibouti, Africa/Douala, Africa/El_Aaiun, Africa/Freetown, Africa/Gaborone, Africa/Harare, Africa/Johannesburg, Africa/Juba, 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 America/Adak, America/Anchorage, 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/Salta, America/Argentina/San_Juan, America/Argentina/San_Luis, America/Argentina/Tucuman,
America/Argentina/Ushuaia, America/Aruba, America/Asuncion, America/Atikokan,
America/Bahia, America/Bahia_Banderas, 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/Costa_Rica, America/Creston, America/Cuiaba,
America/Curacao, America/Danmarkshavn, America/Dawson, America/Dawson_Creek,
America/Denver, America/Detroit, America/Dominica, America/Edmonton,
America/Eirunepe, America/El_Salvador, America/Fort_Nelson, America/Fortaleza,
America/Glace_Bay, America/Godthab, 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/Tell_City, America/Indiana/Vevay, America/Indiana/Vincennes, America/Indiana/Winamac,
America/Inuvik, America/Iqaluit, America/Jamaica, America/Juneau,
America/Kentucky/Louisville, America/Kentucky/Monticello, America/Kralendijk, America/La_Paz,
America/Lima, America/Los_Angeles, America/Lower_Princes, America/Maceio,
America/Managua, America/Manaus, America/Marigot, America/Martinique,
America/Matamoros, America/Mazatlan, America/Menominee, America/Merida,
America/Metlakatla, America/Mexico_City, America/Miquelon, America/Moncton,
America/Monterrey, America/Montevideo, America/Montserrat, America/Nassau,
America/New_York, America/Nipigon, America/Nome, America/Noronha,
America/North_Dakota/Beulah, America/North_Dakota/Center, America/North_Dakota/New_Salem, America/Ojinaga,
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/Scoresbysund, America/Sitka,
America/St_Barthelemy, America/St_Johns, America/St_Kitts, America/St_Lucia,
America/St_Thomas, America/St_Vincent, America/Swift_Current, America/Tegucigalpa,
America/Thule, America/Thunder_Bay, America/Tijuana, America/Toronto,
America/Tortola, America/Vancouver, America/Whitehorse, America/Winnipeg,
America/Yakutat, America/Yellowknife
Antarctica Antarctica/Casey, Antarctica/Davis, Antarctica/DumontDUrville, Antarctica/Macquarie,
Antarctica/Mawson, Antarctica/McMurdo, Antarctica/Palmer, Antarctica/Rothera,
Antarctica/Syowa, Antarctica/Troll, Antarctica/Vostok
Arctic Arctic/Longyearbyen
Asia Asia/Aden, Asia/Almaty, Asia/Amman, Asia/Anadyr,
Asia/Aqtau, Asia/Aqtobe, Asia/Ashgabat, Asia/Atyrau,
Asia/Baghdad, Asia/Bahrain, Asia/Baku, Asia/Bangkok,
Asia/Barnaul, Asia/Beirut, Asia/Bishkek, Asia/Brunei,
Asia/Chita, Asia/Choibalsan, Asia/Colombo, Asia/Damascus,
Asia/Dhaka, Asia/Dili, Asia/Dubai, Asia/Dushanbe,
Asia/Famagusta, Asia/Gaza, Asia/Hebron, Asia/Ho_Chi_Minh,
Asia/Hong_Kong, Asia/Hovd, Asia/Irkutsk, Asia/Jakarta,
Asia/Jayapura, Asia/Jerusalem, Asia/Kabul, Asia/Kamchatka,
Asia/Karachi, Asia/Kathmandu, Asia/Khandyga, Asia/Kolkata,
Asia/Krasnoyarsk, Asia/Kuala_Lumpur, Asia/Kuching, Asia/Kuwait,
Asia/Macau, Asia/Magadan, Asia/Makassar, Asia/Manila,
Asia/Muscat, Asia/Nicosia, Asia/Novokuznetsk, Asia/Novosibirsk,
Asia/Omsk, Asia/Oral, Asia/Phnom_Penh, Asia/Pontianak,
Asia/Pyongyang, Asia/Qatar, Asia/Qyzylorda, Asia/Riyadh,
Asia/Sakhalin, Asia/Samarkand, Asia/Seoul, Asia/Shanghai,
Asia/Singapore, Asia/Srednekolymsk, Asia/Taipei, Asia/Tashkent,
Asia/Tbilisi, Asia/Tehran, Asia/Thimphu, Asia/Tokyo,
Asia/Tomsk, Asia/Ulaanbaatar, Asia/Urumqi, Asia/Ust-Nera,
Asia/Vientiane, Asia/Vladivostok, Asia/Yakutsk, Asia/Yangon,
Asia/Yekaterinburg, Asia/Yerevan
Atlantic Atlantic/Azores,  Atlantic/Bermuda,  Atlantic/Canary,  Atlantic/Cape_Verde,
Atlantic/Faroe,  Atlantic/Madeira,  Atlantic/Reykjavik,  Atlantic/South_Georgia,
Atlantic/St_Helena,  Atlantic/Stanley
Australia 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 Europe/Amsterdam,  Europe/Andorra,  Europe/Astrakhan,  Europe/Athens,
Europe/Belgrade,  Europe/Berlin,  Europe/Bratislava,  Europe/Brussels,
Europe/Bucharest,  Europe/Budapest,  Europe/Busingen,  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/Kirov,  Europe/Lisbon,
Europe/Ljubljana,  Europe/London,  Europe/Luxembourg,  Europe/Madrid,
Europe/Malta,  Europe/Mariehamn,  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/Saratov,  Europe/Simferopol,
Europe/Skopje,  Europe/Sofia,  Europe/Stockholm,  Europe/Tallinn,
Europe/Tirane,  Europe/Ulyanovsk,  Europe/Uzhgorod,  Europe/Vaduz,
Europe/Vatican,  Europe/Vienna,  Europe/Vilnius,  Europe/Volgograd,
Europe/Warsaw,  Europe/Zagreb,  Europe/Zaporozhye,  Europe/Zurich
Indian Indian/Antananarivo, Indian/Chagos, Indian/Christmas, Indian/Cocos,
Indian/Comoro, Indian/Kerguelen, Indian/Mahe, Indian/Maldives,
Indian/Mauritius, Indian/Mayotte, Indian/Reunion
Pacific Pacific/Apia, Pacific/Auckland, Pacific/Bougainville, Pacific/Chatham,
Pacific/Chuuk, 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/Pohnpei, Pacific/Port_Moresby,
Pacific/Rarotonga, Pacific/Saipan, Pacific/Tahiti, Pacific/Tarawa,
Pacific/Tongatapu, Pacific/Wake, Pacific/Wallis
Others Africa/Asmera, Africa/Timbuktu, America/Argentina/ComodRivadavia, America/Atka,
America/Buenos_Aires, America/Catamarca, America/Coral_Harbour, America/Cordoba,
America/Ensenada, America/Fort_Wayne, America/Indianapolis, America/Jujuy,
America/Knox_IN, America/Louisville, America/Mendoza, America/Montreal,
America/Porto_Acre, America/Rosario, America/Santa_Isabel, America/Shiprock,
America/Virgin, Antarctica/South_Pole, Asia/Ashkhabad, Asia/Calcutta,
Asia/Chongqing, Asia/Chungking, Asia/Dacca, Asia/Harbin,
Asia/Istanbul, Asia/Kashgar, Asia/Katmandu, Asia/Macao,
Asia/Rangoon, Asia/Saigon, Asia/Tel_Aviv, Asia/Thimbu,
Asia/Ujung_Pandang, Asia/Ulan_Bator, Atlantic/Faeroe, Atlantic/Jan_Mayen,
Australia/ACT, Australia/Canberra, Australia/LHI, Australia/North,
Australia/NSW, Australia/Queensland, Australia/South, Australia/Tasmania,
Australia/Victoria, Australia/West, Australia/Yancowinna, Brazil/Acre,
Brazil/DeNoronha, Brazil/East, Brazil/West, Canada/Atlantic,
Canada/Central, Canada/East-Saskatchewan, Canada/Eastern, Canada/Mountain,
Canada/Newfoundland, Canada/Pacific, Canada/Saskatchewan, Canada/Yukon,
CET, Chile/Continental, Chile/EasterIsland, CST6CDT,
Cuba, EET, Egypt, Eire,
EST, EST5EDT, Etc/GMT, Etc/GMT+0,
Etc/GMT+1, Etc/GMT+10, Etc/GMT+11, Etc/GMT+12,
Etc/GMT+2, Etc/GMT+3, Etc/GMT+4, Etc/GMT+5,
Etc/GMT+6, Etc/GMT+7, Etc/GMT+8, Etc/GMT+9,
Etc/GMT-0, Etc/GMT-1, Etc/GMT-10, Etc/GMT-11,
Etc/GMT-12, Etc/GMT-13, Etc/GMT-14, Etc/GMT-2,
Etc/GMT-3, Etc/GMT-4, Etc/GMT-5, Etc/GMT-6,
Etc/GMT-7, Etc/GMT-8, Etc/GMT-9, Etc/GMT0,
Etc/Greenwich, Etc/UCT, Etc/Universal, Etc/UTC,
Etc/Zulu, Europe/Belfast, Europe/Nicosia, Europe/Tiraspol,
Factory, GB, GB-Eire, GMT,
GMT+0, GMT-0, GMT0, Greenwich,
Hongkong, HST, Iceland, Iran,
Israel, Jamaica, Japan, Kwajalein,
Libya, MET, Mexico/BajaNorte, Mexico/BajaSur,
Mexico/General, MST, MST7MDT, Navajo,
NZ, NZ-CHAT, Pacific/Ponape, Pacific/Samoa,
Pacific/Truk, Pacific/Yap, Poland, Portugal,
PRC, PST8PDT, ROC, ROK,
Singapore, Turkey, UCT, Universal,
US/Alaska, US/Aleutian, US/Arizona, US/Central,
US/East-Indiana, US/Eastern, US/Hawaii, US/Indiana-Starke,
US/Michigan, US/Mountain, US/Pacific, US/Pacific-New,
US/Samoa, UTC, W-SU, WET,
Zulu