We went to Sea World a few weeks ago, and it was miserably hot. I didn't find it to be a good hot weather park at all. We were there at opening, and my daughters rode Kracken twice, Journey to Atlantis once, we saw Blue Horizons and Believe, ate lunch at the "healthy options" restaurant, looked at the dolphin nursery, and fed the dolphins some fish. By 2:30pm we were all exhausted, so we went back to our hotel (Renaissance across the street) and had a long nap and ordered room service.
I love Sea World, but from now on it will be a cooler weather option for us. Even though we sat down and were covered for the shows, we weren't really any cooler, because after all you are sitting on a big metal-covered set of bleachers in the Florida summer heat heat and humidity. We disn't choose any splash zone seating because we didn't want to walk around with wet clothes and shoes.
Have a great time, and if yours can go all day that will be great!!!! But you might have to slow down a bit or leave earlier than you have planned.