Welcome to planDisney, Maggie!
Like you, I like to maximize my time spent at the parks each day by selecting parks to visit based on which ones have the longest operating hours.
Maggie, I recommend that you make your
Disney Park Pass system reservations as soon as you purchase your
theme park tickets. Although you may not know the published park hours at this time, reserving your theme parks early ensures that the parks do not book up for the dates that you are visiting. Once park hours are released, you can then go ahead and cancel your existing reservations and make new selections, as long as there is
plenty of availability.
There is no deadline to make a Disney Park Pass system reservation. In fact, you can even make reservations the same day that you wish to visit, provided that there is availability, of course.
I hope that this answered your question, Maggie!
Happy planning!
Sarah B.