If you entered your Gold Plus number on Priceline you should be able to modify it, the price may change but the rate should be the same. The other question is how much different is the drop off time going to be and is it still the same number of days? For instance if you're picking up the car at 3pm on arrival day and were planning to drop it at 10am on departure day, if you drop it anytime before 3pm it would be the same number of days and the price wouldn't change. If you're picking up at 10 am and were planning to drop at 10am, any later time is going to be charged for. Usually hourly for the first three hours, then daily. At whatever rate is in the rental agreement.