Changing the time zone is easy in PHP. To change the time zone, you can use putenv function passing the target time zone like this
<?php
putenv("TZ=Europe/London");
?>
If you want to change the time zone on a single page, use this function at the top of you script and if you want change the time zone for all page. Use it inside your configuration file or a file which is included in all of your PHP scripts.