computer3gold, you only need one timer, and that is the pacific one, because they will all be released at the same time, just different times in the time zones, so actually for the other time zones, you will be giving a wrong time.
The timers is based on your system clock.
After you select your correct time zone, the end of the timer will be equivalent to Midnight in the pacific time zone.
For example, Eastern Time will reach midnight 3 hours before it is midnight in San Francisco so each time zone timer must be set for the San Francisco Time zone equivalent for their time zone.