Generally, "days" as far as car rentals go have to do with 24 hour periods and not calendar days, in my experience. So waiting until after midnight won't save you anything in terms of the number of days you are charged for. If you had an arriving flight at, say, 1pm and the departing flight at 6pm like you have, it might make sense to hang out in the airport for a while after you land before picking up your car or planning to bring it back early enough on your return day or both to keep from getting dinged for an extra day. I know that terminal 4, which Spirit uses, has free high speed wireless internet, so burning up a couple of hours there is easily done. Since your flight comes in so late, if you do decide to use priceline, I will say that by making one bid before midnight and one after midnight, you might be able to get some extra bids in without waiting 3 days or whatever the required time currently is. I have done this many times in the past, but they may not allow this any more. Last year, not long after posting about this trick on this site, I was denied an extra bid using that method. It made me wonder if PL people were monitoring what was said here to close loopholes they didn't want used. I took a quick look at sidestep and saw cars for your dates in the low 30 dollar range. Hertz was the lowest, but it said it was off airport. Since you can cancel and might be able to use a code or coupon to get a discount and you wouldn't have to pay a priceline fee, it seems you should try some of the other board links to book a car directly. There is also a site called carrentalexpress that i have used many time in FLL. They deal with independent agencies. There are a few there. I looked there for you, but at this time, the options don't seem to be as good. Also, those agencies aren't open as late as the ones in airport, sometimes. If you get a hotel next to the airport for your first night, you might consider using the hotel shuttle the first night and to get back to the airport the next day and get your car then. You might be able to rent for one less day that way, but it might cut into your trip a little, too.