We have a car reserved through Thrifty for Christmas time. Our airline bumped our flight up by 5-6 hours. When I called to change the pick-up time (pick up same day, did not add any extra days as we were to be returning it early) I was told they would change my reservation for the entire 11 day rental period to reflect the current rates. It would have been approx. $100 more. I left it as is in case the flight time changes again.