I have a computers in different time zone. If i make a setting in group policies let say for 8 am, when the computer sees this policy it take effect for 8 am on the computers time no matter what time zone it is in correct?

You post was a little ambigouous......

 The group policy will be pushed out to all Computers at the next interval (default 90min?) then at this point the policy will be on the local machines.

If, you have a policy that is actually set up to do something at 8am, then it will happen on the local machine when the time on that machine hits 8am.

 Hope that answers your questions :)