It varies depending on if the resaraunt is in a theme park, a resort, or if the theme park is an early opening.
For the themeparks
Most of the breakfast open at 8:00 and run through to 11:30
Lunches are usually from about 11:30 through 4:30.
Dinner from 4:30 onwards. Usually the shops are open 1 hour after the rides close so anyone having a seating time 1 hour before the parks are officially closing should be able to complete their meal without a problem.
Some themepark restaurants ( like Crystal Palace) will actually still be serving breakfast as the lunch guests come in.
In the resorts the (non character) breakfasts would be open earlier and dinner service usually starts/finishes a little later.
