We've driven to and from Orlando from the Tampa airport several times. Has usually taken us an hour.
But, if you are driving to catch a flight, I'd allow a minimum of 90 min. One year (2005), we were driving from the Tampa airport to WDW and it took us 2 hours due to a big traffic jam due to a very bad car accident on the road. So sad about the accident......also, we were glad we weren't driving to catch a flight, but rather to check into our hotel.