Getting in late is actually much less likely than getting in really early; and having to leave early, too. With flights out of Florida, they are infamous for putting you on the 5:45 am flight, meaning that you spend the last day of your vacation waiting in airports or already at home. They also will often use very odd routing, having you fly in the opposite direction from your destination, then reverse course to get where you want to go. (I know someone who got a great price on a flight from TX to FL -- via Chicago! The total travel time, with layovers, was 10 hours.)
Go to to biddingfortravel.com, and read as much as you can before you try bidding. In addition, here are a few other tips:
When using Priceline (or Hotwire) for airfares, you **MUST** allow an extra day at each end of the trip strictly for travelling. I CANNOT emphasize this enough!! If you have to be somewhere at a certain time for something, it means that you must travel the day before. When figuring the cost savings, remember that you are going to have an extra hotel night (and perhaps a car rental day, too) to figure into the total.
It's one thing to blindly stumble around making random Priceline bids for a hotel night, but NEVER do this for an airfare, especially if it is for several tickets. Before you realize that you've done something irreversible, you could find yourself holding a lot of really useless, nontransferable, but paid-for air tickets. (If you mess up a Priceline hotel bid, you can give or sell the room to someone else; you can't do that with air tickets.) Remember, this is gambling, and if you end up with something you don't like, you have no one else but yourself to blame. Priceline is very clear on how the rules work, and they don't negotiate or feel sorry for you if you didn't understand them; caveat emptor.
I don't recommend using Priceline for air travel unless you absolutely have to get somewhere on less than 14 days' notice, and nothing else is affordable. (Think out-of-town funeral, but only if you have time to fly the day before the funeral.) I absolutely don't recommend that your first Priceline bid be for air tickets unless you absolutely have no choice. For flights, I think that Hotwire is the better choice; they give you a price without commitment, and you can choose to take it or leave it.
Here's a tip on Hotwire (Hotwire only; does not apply to Priceline!): sometimes you can guess which flights you are being offered. If possible, use the smallest airports you can fly into or out of, and always check jet only, and no more than one connection; if there are only one or two flights per day, then you have a good idea of what you are getting. If your home airport is a hub; the odds are very high that your flight will be on your airport's hub carrier. My home airport is STL; every Hotwire flight that anyone I know has ever taken out of here has been on AA.
Now, having said all that in that dire tone of voice, let me say that I use both Priceline and Hotwire frequently, but almost never for flights, because I have more money than time. On hotels and rental cars, Priceline is absolutely wonderful, and the savings that we've realized by using them have allowed us to really indulge our travel bug. I've probably bought almost 100 hotel nights on Priceline over the last 3 yrs.
PS: Having posted all this, I went back and realized that the OP was Tinkerbellish. Forgive me, T, but are you not a minor? The minimum age for flight bids on Priceline is 18, for hotel bids, 21, and for car rentals, 25. If you are younger and lie about your age, Priceline will still take your money, but you would have no recourse if the airline, hotel, or car agency refused to serve you.