In my server there are some sites from Turkey, some of from England, some of from Germany. I have got timezone problem in that sites. I found easy solution for this. Just add .htaccess this code:

php_value date.timezone "Europe/Istanbul"

or

php_value date.timezone "America/Chicago"

You can test date is change or not

<?php
 echo date('d-m-Y H:i:s');
?>

If htaccess can't solve your problem, add this code to your php
<?php
putenv("TZ=Europe/Istanbul");
?>
Full List of Time Zone

AD Europe/Andorra

AE Asia/Dubai

AF Asia/Kabul

AG America/Antigua

AI America/Anguilla

AL Europe/Tirane

AM Asia/Yerevan

AN America/Curacao

AO Africa/Luanda

AQ Antarctica/McMurdo

AQ Antarctica/South_Pole

AQ Antarctica/Palmer

AQ Antarctica/Mawson

AQ Antarctica/Davis

AQ Antarctica/Casey

AQ Antarctica/DumontDUrville

AR America/Buenos_Aires

AR America/Rosario

AR America/Cordoba

AR America/Jujuy

AR America/Catamarca

AR America/Mendoza

AS Pacific/Pago_Pago

AT Europe/Vienna

AU Australia/Lord_Howe

AU Australia/Hobart

AU Australia/Melbourne

AU Australia/Sydney

AU Australia/Broken_Hill

AU Australia/Brisbane

AU Australia/Lindeman

AU Australia/Adelaide

AU Australia/Darwin

AU Australia/Perth

AW America/Aruba

AZ Asia/Baku

BA Europe/Sarajevo

BB America/Barbados

BD Asia/Dacca

BE Europe/Brussels

BF Africa/Ouagadougou

BG Europe/Sofia

BH Asia/Bahrain

BI Africa/Bujumbura

BJ Africa/Porto-Novo

BM Atlantic/Bermuda

BN Asia/Brunei

BO America/La_Paz

BR America/Noronha

BR America/Belem

BR America/Fortaleza

BR America/Araguaina

BR America/Maceio

BR America/Sao_Paulo

BR America/Cuiaba

BR America/Porto_Velho

BR America/Manaus

BR America/Porto_Acre

BS America/Nassau

BT Asia/Thimbu

BW Africa/Gaborone

BY Europe/Minsk

BZ America/Belize

CA America/St_Johns

CA America/Halifax

CA America/Glace_Bay

CA America/Goose_Bay

CA America/Pangnirtung

CA America/Montreal

CA America/Nipigon

CA America/Thunder_Bay

CA America/Iqaluit

CA America/Winnipeg

CA America/Rainy_River

CA America/Rankin_Inlet

CA America/Regina

CA America/Swift_Current

CA America/Edmonton

CA America/Yellowknife

CA America/Inuvik

CA America/Dawson_Creek

CA America/Vancouver

CA America/Whitehorse

CA America/Dawson

CC Indian/Cocos

CD Africa/Kinshasa

CD Africa/Lubumbashi

CF Africa/Bangui

CG Africa/Brazzaville

CH Europe/Zurich

CI Africa/Abidjan

CK Pacific/Rarotonga

CL America/Santiago

CL Pacific/Easter

CM Africa/Douala

CN Asia/Harbin

CN Asia/Shanghai

CN Asia/Hong_Kong

CN Asia/Chungking

CN Asia/Urumqi

CN Asia/Kashgar

CO America/Bogota

CR America/Costa_Rica

CU America/Havana

CV Atlantic/Cape_Verde

CX Indian/Christmas

CY Asia/Nicosia

CZ Europe/Prague

DE Europe/Berlin

DJ Africa/Djibouti

DK Europe/Copenhagen

DM America/Dominica

DO America/Santo_Domingo

DZ Africa/Algiers

EC America/Guayaquil

EC Pacific/Galapagos

EE Europe/Tallinn

EG Africa/Cairo

EH Africa/El_Aaiun

ER Africa/Asmera

ES Europe/Madrid

ES Africa/Ceuta

ES Atlantic/Canary

ET Africa/Addis_Ababa

FI Europe/Helsinki

FJ Pacific/Fiji

FK Atlantic/Stanley

FM Pacific/Yap

FM Pacific/Truk

FM Pacific/Ponape

FM Pacific/Kosrae

FO Atlantic/Faeroe

FR Europe/Paris

GA Africa/Libreville

GB Europe/London

GB Europe/Belfast

GD America/Grenada

GE Asia/Tbilisi

GF America/Cayenne

GH Africa/Accra

GI Europe/Gibraltar

GL America/Scoresbysund

GL America/Godthab

GL America/Thule

GM Africa/Banjul

GN Africa/Conakry

GP America/Guadeloupe

GQ Africa/Malabo

GR Europe/Athens

GS Atlantic/South_Georgia

GT America/Guatemala

GU Pacific/Guam

GW Africa/Bissau

GY America/Guyana

HN America/Tegucigalpa

HR Europe/Zagreb

HT America/Port-au-Prince

HU Europe/Budapest

ID Asia/Jakarta

ID Asia/Ujung_Pandang

ID Asia/Jayapura

IE Europe/Dublin

IL Asia/Jerusalem

IN Asia/Calcutta

IO Indian/Chagos

IQ Asia/Baghdad

IR Asia/Tehran

IS Atlantic/Reykjavik

IT Europe/Rome

JM America/Jamaica

JO Asia/Amman

JP Asia/Tokyo

KE Africa/Nairobi

KG Asia/Bishkek

KH Asia/Phnom_Penh

KI Pacific/Tarawa

KI Pacific/Enderbury

KI Pacific/Kiritimati

KM Indian/Comoro

KN America/St_Kitts

KP Asia/Pyongyang

KR Asia/Seoul

KW Asia/Kuwait

KY America/Cayman

KZ Asia/Almaty

KZ Asia/Aqtobe

KZ Asia/Aqtau

LA Asia/Vientiane

LB Asia/Beirut

LC America/St_Lucia

LI Europe/Vaduz

LK Asia/Colombo

LR Africa/Monrovia

LS Africa/Maseru

LT Europe/Vilnius

LU Europe/Luxembourg

LV Europe/Riga

LY Africa/Tripoli

MA Africa/Casablanca

MC Europe/Monaco

MD Europe/Chisinau

MG Indian/Antananarivo

MH Pacific/Majuro

MH Pacific/Kwajalein

MK Europe/Skopje

ML Africa/Bamako

ML Africa/Timbuktu

MM Asia/Rangoon

MN Asia/Ulan_Bator

MO Asia/Macao

MP Pacific/Saipan

MQ America/Martinique

MR Africa/Nouakchott

MS America/Montserrat

MT Europe/Malta

MU Indian/Mauritius

MV Indian/Maldives

MW Africa/Blantyre

MX America/Cancun

MX America/Mexico_City

MX America/Mazatlan

MX America/Chihuahua

MX America/Ensenada

MX America/Tijuana

MY Asia/Kuala_Lumpur

MY Asia/Kuching

MZ Africa/Maputo

NA Africa/Windhoek

NC Pacific/Noumea

NE Africa/Niamey

NF Pacific/Norfolk

NG Africa/Lagos

NI America/Managua

NL Europe/Amsterdam

NO Europe/Oslo

NP Asia/Katmandu

NR Pacific/Nauru

NU Pacific/Niue

NZ Pacific/Auckland

NZ Pacific/Chatham

OM Asia/Muscat

PA America/Panama

PE America/Lima

PF Pacific/Tahiti

PF Pacific/Marquesas

PF Pacific/Gambier

PG Pacific/Port_Moresby

PH Asia/Manila

PK Asia/Karachi

PL Europe/Warsaw

PM America/Miquelon

PN Pacific/Pitcairn

PR America/Puerto_Rico

PS Asia/Gaza

PT Europe/Lisbon

PT Atlantic/Madeira

PT Atlantic/Azores

PW Pacific/Palau

PY America/Asuncion

QA Asia/Qatar

RE Indian/Reunion

RO Europe/Bucharest

RU Europe/Kaliningrad

RU Europe/Moscow

RU Europe/Samara

RU Asia/Yekaterinburg

RU Asia/Omsk

RU Asia/Novosibirsk

RU Asia/Krasnoyarsk

RU Asia/Irkutsk

RU Asia/Yakutsk

RU Asia/Vladivostok

RU Asia/Magadan

RU Asia/Kamchatka

RU Asia/Anadyr

RW Africa/Kigali

SA Asia/Riyadh

SB Pacific/Guadalcanal

SC Indian/Mahe

SD Africa/Khartoum

SE Europe/Stockholm

SG Asia/Singapore

SH Atlantic/St_Helena

SI Europe/Ljubljana

SJ Arctic/Longyearbyen

SJ Atlantic/Jan_Mayen

SK Europe/Bratislava

SL Africa/Freetown

SM Europe/San_Marino

SN Africa/Dakar

SO Africa/Mogadishu

SR America/Paramaribo

ST Africa/Sao_Tome

SV America/El_Salvador

SY Asia/Damascus

SZ Africa/Mbabane

TC America/Grand_Turk

TD Africa/Ndjamena

TF Indian/Kerguelen

TG Africa/Lome

TH Asia/Bangkok

TJ Asia/Dushanbe

TK Pacific/Fakaofo

TM Asia/Ashkhabad

TN Africa/Tunis

TO Pacific/Tongatapu

TR Europe/Istanbul

TT America/Port_of_Spain

TV Pacific/Funafuti

TW Asia/Taipei

TZ Africa/Dar_es_Salaam

UA Europe/Kiev

UA Europe/Simferopol

UG Africa/Kampala

UM Pacific/Johnston

UM Pacific/Midway

UM Pacific/Wake

US America/New_York

US America/Detroit

US America/Louisville

US America/Indianapolis

US America/Indiana/Marengo

US America/Indiana/Knox

US America/Indiana/Vevay

US America/Chicago

US America/Menominee

US America/Denver

US America/Boise

US America/Shiprock

US America/Phoenix

US America/Los_Angeles

US America/Anchorage

US America/Juneau

US America/Yakutat

US America/Nome

US America/Adak

US Pacific/Honolulu

UY America/Montevideo

UZ Asia/Samarkand

UZ Asia/Tashkent

VA Europe/Vatican

VC America/St_Vincent

VE America/Caracas

VG America/Tortola

VI America/St_Thomas

VN Asia/Saigon

VU Pacific/Efate

WF Pacific/Wallis

WS Pacific/Apia

YE Asia/Aden

YT Indian/Mayotte

YU Europe/Belgrade

ZA Africa/Johannesburg

ZM Africa/Lusaka

ZW Africa/Harare
Source : http://iceburn.info/apache/change-the-time-zone-for-an-entire-directory.html