We are often asked this question and here is the simple way to change your timezone in WHMCS so it is different from your server time.
Firstly head over to http://www.php.net/manual/en/timezones.php and find the timezone you wish to use for your location.
For our example, we will use New Zealand.
From the timezones page we can see New Zealand is in the Pacific – so we add the following – Pacific/Auckland.
Open up your configuration.php (which is in your root WHMCS directory) using Notepad ++ or whichever text editor you are using and then at the bottom before the closing php tag add the following line:
Save the changes and the re upload the file. Go to your WHMCS Admin area and log in and your time shown should now display the current New Zealand time, irrespective of what your server time is set too.