My daughter’s cafeteria was open from at least 7 am to 8 pm, all the time. Once you were in the door there were all kinds of stations and you then stood in line for those. Once you were in you could eat as much as you wanted and stay as long as you wanted.
I guess some stations close for restocking at certain times of the day or to switch from breakfast to lunch/dinner entrees, but the drinks, ice cream, soups, salads are always open. They certainly don’t restrict portion size or amount of food you eat.