If you check out the historical hours site, it looks like the third week in Aug is when they start closing earlier. Of course,that's when we'll be there!! I always plan my ps's figuring on the earlier closing times. Studios most always closes no earlier than 9 pm, AK at 5 pm. Epcot (more or less) at 6 pm. MK is the only one that is iffy. So, I figure it will be about 7-8 pm earliest. I make my dinner plans for MK days as late lunches, around 4ish. Sometimes, I don't make ps for MK. If they are open late, I grab something on the run. If they close earlier, I eat at the resort.
One thing I'm hoping will happen here....with the FT pkg bringing in more people this summer, hopefully the parks will remain open longer, especially for the third week. Here's hoping for an e-night or two also.