There is no "grace period" or "3 day cooling off period" or similar law in Florida for returning a used car to the dealer.
However, if there is something wrong with the car, or the dealer engaged in some unfair or deceptive trade practices in selling you the car, you may be able to get relief from a bad car deal.
Consult with a consumer advocate attorney in your area, you can find one here: www.naca.net or you can view my profile on Avvo.
I am an attorney who is only licensed in the State of Florida. My answer is general legal advice based upon what I perceive your question to be, and should not be relied upon because every person's facts and circumstances are unique, and because specific laws vary from state to state. To completely evaluate a legal issue requires reviewing and evaluating all relevant facts, applicable laws and other information. My answer does not create an attorney-client relationship, and offered for informational purposes only.
As usual, Dana is absolutely right. In fact there is no general right to cancel a car sale that any consumer has anywhere that I have ever heard of, but there are lots of laws on how a car dealer is supposed to honestly and fairly sell cars and if one of those is violated those laws sometimes give the buyer the right to cancel the sale. But those laws are also silly different from state to state. So if you want to find a legal way to cancel a car sale when you can't think of one on your own, then your best bet is to talk to a local car sales fraud or consumer law attorney near you. Local lawyers know local laws. In Florida, if you are anywhere near Dana Manner at all, then I think he is the man to talk to. To find his contact info, or another consumer law attorney near you, go to www.USLemonLawyers.com. Lawyers don't pay to be listed on that national directory and most of them are members of the only national group of consumer lawyers in the US, Naca.net. If this answer was helpful, please give it a Vote UP review below. And be sure to mark what you think is the best answer you get so we can all be sure we are doing a good job for people (my vote is for Dana). Thanks for asking and good luck.
This answer is for general purposes only and does not establish an attorney-client relationship. The law in your state may differ and your best answer will always come from a local attorney that you meet with privately. If you need a Consumer Law attorney, click the link above to find a Consumer Law attorney near you.
You're going to need a "legal" reason to back out, not just an "I changed my mind" kinda reason. Good luck with it...