The event usually starts at 6:30, they let you into the park for "Stay and Scream" where you are in the park for the day (meaning you have spent the day in the park with an additional ticket and just hang out while they convert it the rest of the park) and they let you into the houses about an hour before they open the front gates. In the past they have had the events at both parks, last year it was only at the studios, though they did open portions of IOA during the really busy times. This year, I suspect, the event will be at USF.