IME the hotel has to ask you if they want to charge anything more than what I booked. For instance, if I had a rate of $110 for Monday night, if I showed up Monday at 6am, they could either just give me the room （actually happened once, though it was an ORD airport hotel a couple days before Christmas) or tell me exactly what additional amount I would need to pay to receive the room then instead of at the official check in time. If the hotel doesn't say when you check in that they're charging you extra, then they have no grounds to do so.