I would always try to make a 7 am appt at K Street (they do try to fit you in as a walk-in if needed), and get there like 15 or 10 minutes before and be the first in line. There's usually a line waiting for the door to open. If you can be one of the first, yes, you can get out in 20 minutes or so. But otherwise it can be a little slower, as PP said, as that is a busy time.