When doing Disney World, yes it's important to pace yourself, but also consider that the best times to be at the park are right when it opens and after dinner. The weary tourists from the west sleep late given the east coast time zone, and the parks don't get crowded until late morning. Then they're beat by dinner, so the park crowds thin at around 6-7pm until close. Get up early, do some activities, then head back to the resort to take a nap before returning. This way you'll also obviate the harsh UV indexes of the afternoon. With all that said, the festival of fantasy parade at magic kingdom (3pm) is amazing.