You have to be careful because it is VERY hot in the summer, so it is not really their high season.
You also have to be careful of when they have their holidays such as Thanksgiving etc.
I went in February a couple of years ago and it was great. Weather was high 70s but never really too unpleasant. (I think we were lucky though, it is not always that warm in February).
They do have Presidents day holiday during February so theme parks were packed that weekend, but either side of that they were fine.
Search Google as there are loads of sights about visiting Florida giving suggestions for the better times to go.