The heat is not so bad, the humidity will really surprise you.
The first year I went was in May and I spent almost the entire trip in the Dolphin doing presentations to drunk senior managers, sigh. However on the last day two of us slipped away and hit the parks in the rain. It was great I don’t think we waited for anything, and once you are soaked it doesn’t matter anymore how much it is raining ( It’s a warm rain! )
The next year we had a lot more time to ourselves and it was HOT, CROWDED, and HUMID. That was the trip that made me realize that one of my dreams, working at WDW, would never come to pass.