It will be the same as it is now. The restaurant will find ways to get you to leave if you only spend $10 and stay another 2 hours. The amount you stay is directly proportional to how much you spend. If you stay 5 hours but you bought a $10,000 bottle of Screaming Eagle then don't expect to hear a peep from the restaurant.

I've long felt that if you're not on time for your reservation then you get sidelined and accommodated when it is convenient for the restaurant. I understand things happen but unless you call in advance and explain that you're going to be late then you're really just not respecting the restaurant's time and they should not have any obligation to you.