Yup - park hours will change as you get closer to your trip different and events - fireworks/evening shows may change as well. Put your dinner plans where you want them and then just work around them. The really only big issue is if you were to book a PPO 8:00am breakfast in hopes to get in before anyone -- if opening is at 9am then great it will work, but if they happen to change opening to 8am then you lose any advantage. The only thing about this is that you can cancel your breakfast as long as it is with in their cancellation policy - usually by 11:59pm the night before. Your best strategy is to book multiple reservations where you think you might be, so if it is a toss up between MK and Epcot book a reservation at each and then as they release the hours pick which reservation will fit with your plan and cancel what you don't need. It stinks doing it this way, because you are technically holding a reservation from someone else, but it is tough to plan when you really don't know what the park hours will be. I will always cancel what i don't need as soon as i figure out my plan (usually only holding a reservation for a week) which odds are it will be scooped up by someone if it is a hot reservation.