When is the shop quietest for walk-ins?

Tuesday to Thursday before 11:00 is the quietest time; you will usually wait less than fifteen minutes (sample).
Friday after 16:00 and Saturday between 10:00 and 14:00 are the busiest. If you want a set time on a Saturday, book a chair.
Walk-ins close an hour before the shop does, so the last names on the board still get a proper cut.