we just got back last week. with sea world, you get the second day free option. it was so worth it. the first day, we went to all the shows. the second time, we let the kids play all they wanted in the fountains and water play area. we were there probably 5 hrs each time. i'm sure you could do the whole park in 6 hrs, give or take a few things, but it's so much more realxing to go for the 2 days.
also, this site has a seaworld section that can answer a lot of questions for you too.