Hi alliecats! I don't know how late they are open, but we ate at the Dolphin Fountain twice and really enjoyed it. They have very good burgers and delicious ice cream. I don't think they're open very late though, because I remember walking past once or twice after they had closed. I'm just guessing here, but maybe 9 or 10. Tubbi's is right down the hall though, and they are open 24 hours! You can get burgers and other sandwiches at Tubbi's, but I would recommend the pizza - very good, and not expensive at all.
We didn't eat at Splash, but I can tell you they have very good drinks!

You probably know this, but it's Splash is the poolside bar/grill, so I'd say they close pretty early.