It is very common for F! to start a half-hour after the park has "closed."
The "close" time refers to the time when the other attractions in the park stop admitting new guests into the queues.
Guests who are still in the queues can wait until it is their turn to ride, even though it is after the park's closing time.
Most guests wanting to see the 9PM F! will already be in the theater by 8:30, or so, anyway.