i did it a couple of years ago arriving at 5pm Saturday (multiple flights). It took 10-15 minutes just to get to the front of the GE line and then you have to ask the officer to put you on a written list. The total wait was at least 60 minutes. Probably the last thing you want to do after a 12-hour flight but really there is no choice when there were zero appointments online at SFO. If that has changed now it would be fantastic. But for years it was literally zero appointments.