For right now, it looks like they have the parks staggered by 1 hour for morning openings and evening closings. So Epcot is the latest to open at 11am, but also the latest to close at 9pm (probably due to the fact they have the most restaurants). Each park is open 10 hours. My guess is this is mostly due to park transportation/busses so they can go heavy on AK busses early, then switch those busses to HS/E routes later for example. It's probably a safe assumption that those hours will change as things start to normalize, more workers are called back, and capacity increases, but as to when that happens is completely unknown. I look at it as those are the minimum hours the parks will be open.