According to Google Maps, it's about 1 hour and 20 minutes to get from Tampa to WDW. So allowing about an hour to get luggage and the rental car, you'll probably get to WDW around 3:30 pm (maybe a little later if there is traffic). Check-in and dropping off stuff would be another hour. Then head over to DTD. I would guess that you'd be able to make it, but there might not be a lot of slack room. If they have a later time, I'd grab that. If you get in early, you can always go check out DTD (assuming you're going to the RFC at DTD and not the one at AK) before dinner. There is lots to see and do and it can easily eat up time.