we're going to a third birthday tomorrow for about 2 hours. it will overflow. we've been asked to come around early (DD and the bday boy are besties) and there is a housewarming after dinner so we'll stay for that. i think you only really need to limit if you think people won't leave when you're ready. most people start looking to leave after cake is done, so you just time your day as you see fit with stuff like that if you don't want a regimented finish time