There's probably a private company event or some sort of grad night. I went on a day where there was a company event where USF closed at 6 and Islands at 7. They were pretty strict about kicking guests out that weren't part of the event. I initially thought the short hours would deter people from coming but both parks were pretty busy. A lot of rides had a 40-60 minute wait. If you don't have EP I would go to USF first and knock out what you want to do there before heading over to Islands. If you don't have a park to park ticket I would just stick to Islands.