From my point of view, +1 to Ozrider.

Beyond that here is the way it worked at the Velomeister.

If you unloaded a broken bike from your car into the shop, it went into the repair que, with a vague over estimated time for repair and a promise of a call with a more definitive timeline.
Bikes that had been purchased from us went to the head of the line and all bikes got a preliminary checkout to see exactly what was needed. Calls were placed and decisions were made about special order parts and authorizations for any additional necessary work. After this part of the process the bike was added to the work flow chart and any specialty tasks were assigned to the appropriate wrenches. Warranty work took presidents over all other waiting bikes except for team bikes. In this case a chain ring replacement would mean replacing the part, a moderate cleaning and a tune-up that would probably included cables.

If you walked your bike into the shop in your riding clothes with a minor problem like a bent chain ring or needing a spoke or a wheel true every effort was made to get you back on the trail in a timely manor. If you brought coffee for the employees you could most likely have your pick of a replacement ring from the drawer of used rings. This type of repair got you just the repair, and this 20 min. repair might take an hour of 5 min at a time work. If the floor was slow and you were a regular customer, in all probability a sales person might do the work if there was a spare work stand available.

This of course is a glossed over simplified version of the inner workings of the shop.