The correct answer, as you found out, it: It depends.

If you wanted the same thing done on a Saturday afternoon in the last week of may it most certainly would not be done the same day. If you bring it in on a thursday in the last week of November then your chances are good.

I drove to the next town to get my son's new bike its first tune-up a few weeks ago. They told me on the phone before that they may have a chance to get it done the same day while I ran errands around town. Well I came back a few hours later and they had not had a chance to get it done yet, so no problem, I went back home... My wife told me as I walked in the door that they had called 5 minutes earlier and the bike was done.