they did that to me one time, I just told them there's no way I brought it late and they took it off. I use to go there like 3 times a week and rent stuff anyway, so I guess they figured it would be better to let it slide than lose my business.
Plus, I get SOOO many free rentals from there that I wouldn't even care much if I paid a late fee once.
BTW, in case anybody didn't know, when you keep a video late, they automatically charge you for another rental, so you might as well keep it for a whole extra rental period since you're gonna pay for it anyway.