I walked right into that place last Saturday. I don't know if it was just luck or not. I got there at 4:40 (they open at 5:00 for dinner). She took my name and said it could be up to an hour wait and did I mind. I said no, I don't mind. So she handed me a buzzer. I said, "So wait, does this mean I can definitely get seated?" She said, "Yes, we can always get you in." So then I asked her how far we could walk with the buzzer. She told me the same floor, but they always try and get the walk ins quickly. I got the buzz 10 minutes later before they opened.
So I don't know if it was luck or not. But the impression I got was that if we got there just before opening, we'd usually be able to get a seat.
It makes me wonder if that worked at other places like O'Hanas. I don't know if they close before dinner or stay open all day. I figure I'll have to try it one day.