We drove from Dallas and it took 17.5 hours and we did slightly above the speed limit. Took us 14 hours to get to Lake City FL where I10 and I75 intersect. I would think it would be about the same or less for you since all you have to do is jump on I10 and straight shot across LA, MS, AL, Panhandle of FL (YUCK...that stretch of I10 at night isnt fun)
We had to go to Jackson MS then angle down to Mobile AL. We easily could have made it there in one day but we were past the cancelation time on our hotel.
Thanks! Actually I'm thinking of doing the drive in reverse - and not actually from Orlando, but rather Lady Lake (about 50 minutes north of Orlando) to Austin..
And thanks for reminding me about the time change - I forgot all about that!