That still doesn't change the fact that there's 24 different time zones. Useless comment.
Ok, I'll try to make it more simple, just for you:
One time group would be for East Asia, Australia and Oceania,
another would be for Europe, Middle East and Africa,
and third would cover both Americas.
You don't need 24 GM's for 3 groups (zones), do you?
If you still have questions, feel free to ask.