If you can not return your car at the agreed drop-off time, the first thing to do is to inform the car rental provider. If you will be arriving just an hour or two after the original drop-off time, it might be possible to drop off the car later than originally agreed. However, in this case, you will be charged for a full extra day. If you are more than two hours late or do not give prior notice to the rental company, you will be charged for one more day and might also be charged a fee for failing to return the car at the originally scheduled time.