Well, it's not definite that you'll be paying more.
If you have already paid a weekly rental rate and your rental is only 5 or 6 days long, it's possible you'll pay no more, because the same weekly rental rate usually applies for rentals of 5 to 7 days. But you should double-check with Dollar and rebook the rental if that's the case.
What time are you collecting the car when you pick it up? If it's 5:00 or later, turning the car in at 5:00 on the final day should incur NO extra charge, because rental days run on a 24-hour basis.
If you pick up at 4:00 or earlier on the first day, you'll definitely be paying extra to turn it in at 5:00. For the first couple of extra hours, you'd pay an hourly rate. Past that you'd pay for an extra day.
As a previous poster said, you can return the car up to 23 hours late without the rental car company being worried about it. At the 24 hour mark they'll start trying to track you down and charging you extra late fees.
Mary
MouseSavers.com