If you leave JAX at 1:00 (assuming a noon arrival, retrieval of luggage and rental car) the traffic up north will be fine. You'll hit the beginning of Orlando rush hour around 4:00. As long as you are through Orlando by around 4:00, you'll be fine.
If you are running late, I'd strongly suggest getting off I-4 at Altamonte Springs and having a liesurely dinner--you'll find a bunch of chain restaurants including Red Lobster, Macaroni Grill, etc. as you head west on Route 436 (east Semoran). By the time you finish between 6:00 & 7:00, the worst of the traffic will have eased.
Anne