Sounds about right. The parks close early, but, crowds are very light, and all rides are usually working at this time, even the water rides. Temps are 55-75, perfect weather most of the time. Wear long pants with a light jacket in the morning, then in the afternoon, you can take off the jacket.
When the parks close at 6pm, you go to dinner and relax.
The other thing to remember, is the parks still open at 9am sharp, and it's a ghost town. This is the perfect time to take a lap of walk on rides. You can get thru all of IOA before noon, then head over to USF.