Just a couple weeks ago, I had an aisle seat for a LAX-JFK, but it was in the middle of Y cabin (19C). Seat map showed the cabin full except for 2 open seats.
At the 24 hour mark, I went to OLCI, and at that moment 6-8 seats opened up, including 15D, which I nabbed.
Prior to that, sometimes I did OLCI, and other times I waited until I got to airport. Now I'm a convert.