Agree, school starts on August 20th. Before that the parks will be very busy, but they do stay open until 10pm.
After that they close early, 9pm, then 8pm, but the crowds are less.
I tell everyone to do the two visit approach. Arrive the parking garage at 07:45am, tour a park, leave in the afternoon, come back at night.
Many like to sleep in because they're on vacation. They get a late start, eat breakfast, take their time, all show up at 11am and this is the worst time to arrive. In the busy summer months, the park actually opens at 08:30am, but they don't say it, just happens. So if you arrive the parking garage at 07:45am, and get in line at the gate, you'll have about 2 hours of short waits before the herd of people arrive.
Many people don't know this, but there's no rope drop like they have at Disney. The order you stand at the gate is the order you enter the park. So if you go in first, you have the entire park to yourself for a few minutes.