umm a timezone feature? I have two ideas how this can be done.
1. Upgrade your PHP to version 5.3.0+. In PHP 5.3.0+, there are lots of new date/time functions that were previously unavailable in PHP 5.2.x or earlier versions. Not sure if it will help with timezone, but its worth trying. However, most shared host do not allow PHP upgrade, so...
2. Use cronjobs.