That depends entirely on the state you buy the used car in and whether that state has laws in place that make a dealer have to offer 3 days to return the used car.
Some states do force a used car dealer to allow you to return a used car within 3 days after purchasing while some states do not require the dealership to allow you to return the used car within 3 days.
Most used car dealers either way though will allow you either 1 to 3 days to return a used car which also known as a cooling off period.
When you buy a used car always ask the dealership if you have a certain amount of time where you can return the used car after purchase.