You can do it in one day, but sometimes it is difficult to see all the shows in way day due to the schedules and location in the park. I have found when trying to cover too many shows in one day, I feel like I am spending all the time walking back and forth across the park. Whenever people visit and want to see Sea World, we normally allow for 2 days, as you can usually get your One Day pass validated to use again within 7 days. I know they have had that offer, and I believe when we were there this week, I saw the line of people at the end of the day getting their tickets validated.
As another poster mentioned - Blue Horizons the new dolphin show is not to be missed, and we always love the Sea Lion Show - Clyde and Seamore. The mime is hilarious, and the bad jokes just give you a reason to laugh!!! We enjoy spending time by the sea lions - they are just plain entertaining. The dolphin nursery is a good spot to spend a few minutes - watching the mothers and calves. Don't miss the Sky Tower - it gives you a great aerial view of the park - it is $3.00 additional. The Odyssea show is very cool - acrobatic type show - think Cirque de Soleil in less than 30 min. We had not eaten at the Shark restaurant before, but did that the other night as well, I had soup and a salad, and was quite pleased. My neighbor works there, and I hear the food is very good. It tends to be crowded during the busy times, be we were there on an slow night to see the Christmas display/shows.
Anyway - we do love Sea World, it's a different experience than Disney, but I think worth the price of admission! If you are into rides, they are limited, but I enjoy watching the animals!
