Hello i was wondering if when buying annual passes when is it valid to be used?

Depends on the pass you buy. Some have blackout dates

Great park for annual pass The fun never gets old.

The day you purchase it. Good and silver there is no blackout dates and bronze as Andrew mentioned above

With a bronze annual pass you can go every day of the year except January 1, April 13, July 4, 14, 16, 21, 23 and December 30.