Always better to make a reservation.. in my experience, i see them get booked a couple of weeks in advance.. you could get lucky during non-peak hours, but it doesnt hurt to have a table booked..
Yes, walking in is much easier during the early or later hours. They take reservations on OpenTable and usually have most of the their reservations up. If they dont have any reservations you may be waiting from 30mins to an hour on a busy Sunday
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