I believe the last reservation offered is 5 minutes before the park closes to regular guests. So for Jollywood, HS closes at 7:00 pm for normal guests.
ADRs can be made for times up to 6:55 pm, assuming that you can get that time when you book. At 7:00 they'll start ushering people out and even blocking off certain paths.
At least this is how they did it last year