SeaWorld can be an all day park, depending on when you go. If you go during the off season, you'll be out of the park by 6pm because that's when it closes. If you go during peak times, it does take the entire day to see and do the park, that is, unless you tear through the park and doing that means you can't enjoy it because you're too stressed to enjoy it.
You need to get to the park at opening and plan your day. I'd suggest going to SeaWorld's website ahead of your trip to get the showtimes via the internet and plan ahead. If you do this, you might be able to squeeze everything in. Trying to do it all and go to a mall and eat might cut your Shamu day short!
If you want a decent dinner, eat at Shark's Underwater Grill at SeaWorld. It's a great place to eat and the atmosphere is really cool.
I highly suggest the water ride Journey To Atlantis and the coaster Kraken. All of the shows are quality, but Clyde and Seamore is the best show in the park.
Have fun.