I usually arrive around 5-10 minutes early for a booking, and at most I wait 5 minutes over the booked time.
For times when there's going to be a delay of 15 or more minutes, shop reception have messaged me letting me know, so at least I don't have to spend the wait time in there and can do other stuff on the way instead.
I always book, so if I turned up and nothing was communicated to me, I'd probably leave after 10 minutes too.

