The owner of the shop I take stuff to tends to underestimate how long things take, so when it's the day after he said it would be done, I'll often drop him an email and say, "Hey, I have some free time this afternoon to come and pick up the bike. Is it ready?" And often the response is "Just finishing up", which I think means "We're starting on it now"
But they do good work and most of the bikes they handle are WAY nicer than what I bring him, AND most of the customers are WAY faster than me, so I figure he must know something!
BTW, I suspect the reason he underestimates the time things take is he also underestimates how many "while you wait" jobs he does. A couple times I brought in one or two wheels for them to true, and said I was happy to leave them and come back another day, but he slapped them on the truing stand and did them there and then.