We've gone many times without a reservation but you will have to wait, and you run the risk of having to wait a long time. As someone mentioned, it can be like 90 minutes.
If you go closer to the end of the evening they may be able to seat you faster, or run the risk of them saying they have no more space for the evening, they base it on ADRs too.
Sometimes if you are willing to sit at the counter, they can get you in faster. Booths (when available - there are only 3 booths) are usually reserved for those with ADRs.