When renting a car, we normally put in the date and time for pickup and dropoff. I have found that it generally makes more sense to use full 24 hour periods.

For example: I plan on renting a car at 9:00AM on Monday and returning it on 6PM Tuesday, a total of 33 hours and charged as 2 days.
However, I normally put the return time as 9:00AM Wednesday morning, a total of 48 hours, with the same 2 day charge.

Why? Well, if I am delayed and am forced to take a flight the next day, I still have my car until 9:00AM the following morning. Or, if the airline contacts me that the flight has be changed or cancelled, perhaps due to weather, I again have the car until the following morning.

This does NOT work if you are on some time-restricted rate (such as a Weekend rate that requires the car to be returned before midnight on Monday). Other than that, it's nice to know you have the car for the additional time if needed without going through the possible hassels of trying to extend the rental another day. Plus, the car rental company will be happy if you bring it back earlier than you stated on the conttract since they are still getting the same amount but can re-rent the car sooner!

Mr Kendall