Here is how you can find the difference between two different timezones
<?php
// Set time to UTC
date_default_timezone_set("UTC");
$utc = date("Y-m-d h:i:s A"); // Get current time as per UTC.
date_default_timezone_set('Australia/Sydney');
$set_timezone = date("Y-m-d h:i:s A"); // Get current time as new timezone.
$difference_in_timezone = (strtotime($set_timezone) - strtotime($utc)) / 3600;
?>
The above code will return 11 as the difference between UTC and Australia/Sydney.
Here is a List of supported timezones
// Set time to UTC
date_default_timezone_set("UTC");
$utc = date("Y-m-d h:i:s A"); // Get current time as per UTC.
date_default_timezone_set('Australia/Sydney');
$set_timezone = date("Y-m-d h:i:s A"); // Get current time as new timezone.
$difference_in_timezone = (strtotime($set_timezone) - strtotime($utc)) / 3600;
?>