Disney dad Says..............................You'll be fine.
I would not go from Safari straight to Kali, it will be too early. If you have young ones do that Wildlife Express Train thing, and walk the Pangani Forest Trail. Maybe see Flights of Wonder, and walk Maharajah Jungle TRek.
Then grab lunch at Tusker House. After lunch you need to decide, is it really hot? If yes, then do Discovery Island attractions.
If it's not too bad, then do Kali to get wet and head for Dinoland.
Hit Primeval Whirl, and Tricera Top Spin, and send a volunteer to get FP for Dinosaur. By the time you are done with the rides you should be dry and your FP's should be ready. If not kill some time at the Boneyard.
If you picked it's not too bad, then do Discovery Island, and you've done most of the park!!!
If you picked I'm boiling here, then after Discovery Island leave and do the rest of the plan in the morning of a return trip.
And heat is relative, Orlando at 90 with it's humidity, is no worse than a dry Sacramento heat at 105.
And let me tell you, I hate heat, but when Sacramento hits 105, I'll be out side for as long as 10 to 12................... minutes!!!!!
You hit the head of the nail, when you said it will be hot everywhere. Enjoy your trip!