Damn. Let my comment publish 4 hours late and I missed this thread.

Absolutely check out Harry Potter land (as klein linked below). They just re-vamped it and added on even more room. I visited it 3 or 4 times within the few years that it opened. I haven't been to the parks since either of it's two major expansions. I bet you could spend a good part of your day in there.

Tips from a local:

1. Bring an umbrella. Florida always has summer showers that are as fickle as it is hot (usually once or twice per day around 4PM).

2. This sounds like a plug, but get those Fast Passes if you want to get the most out of your day. It's summer time so those places are likely packed. Since it sounds like you're going solo though, there's a 'Single Rider' option for rides when attendants (to the ride) are looking for single riders to fill empty spots since people tend to ride in groups. If you ever hear an attendant asking for Single Riders, then grab that chance to skip the line.

3. Islands of Adventure is fun as hell, don't leave that out of your destination.

4. There used to be a regular ol' path-with-guard-rails exit from a Hogwarts ride (the Harry Potter castle) that dumps you out and opposite side of the Harry Potter area entirely. I don't know if that place exists since the renovations, but if you find it, that's how my buddies and I got into the Hogwarts area for free when it first opened. Just act like you have a place to be or left something in the castle if anyone sees you (not like to happen if it's what I remember it being).

5. Enjoy yourself. :)