We generally check in 15 minutes early, but on a few occasions have arrived earlier than that. Some places will allow you to check in, but many others tell you to come back. 'Ohana is one that usually send you away and tells you come back 10 minutes prior. I think it all depends on how the estaurant is doing that night. Busy and backed up? No chance you can check in early. If they are slow or can accomodate you? Why not?