Disney publishes park hours on their website on a rolling 180 day basis. Meaning, you can see park hours today through 7/16 (180 days from today). Tomorrow you’ll be able to see 7/17, etc, etc.
Other planning sites such as Touring Plans and Kenny the Pirate publish park calendars that go further out, presumably from various sources / educated guesses.
Of course, those hours are often subject to change later on.