Don't forget you may also have other costs, such as car hire. Picking one up at around 1500 and dropping off at 1800 will cost a little more. It may also be worth paying for a late checkout so you can have a relaxing last day.
Saying that, you are far more likely to sleep on a flight that leaves at 2040, so could reduce the 'jet lag' feeling and arriving 0950 (0450 Florida time) is so much better for you.