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"
php_value date.timezone "America/Chicago"
You can test date is change or not
echo date('d-m-Y H:i:s');
if you unable to fixed this issue then just add this code in your .htaccess file
Example : SetEnv TZ Europe/London or SetEnv Asia/Karachi or SetEnv IN Asia/Calcutta
Note:Please use only one at a time