I would assume that in most cases, they arent running a mid day update, they would give prior notice that over night X will happen so make sure product is what the label is in the morning.

Being said, I also assume there is some custom-ability to the screens, as in they are probably touch screens or have a a physical button behind the control to allow to cycle through available products to ensure the right product is displayed. That or there is a network controller somewhere on premise (potentially linked to their menu manager) that decides what screen displays what.