To answer your question; it depends. Alternators can be quite different and it will take different amounts of time depending on how difficult it is to remove, replace or clean and install parts in any particular type that you're working on.

A rebuilder will charge accordingly.

I doubt a shop will rebuild an alternator. They are way too cheap to buy.

If you're fortunate enough to have an *auto-electric shop in your town it won't take over an hour and a half to completely overhaul an alternator. Otherwise, your bet bet is to look in your phone book for an AC-Delco parts store or distributor and buy a re-manufactured A-C-Delco Alternator which will have a life-time warranty. Every part inside the re-used aluminum frame is brand new not just the parts that are bad.

Buy rebuilt and do the exchange....quickest and cheapest. The bad ones are sent to Mexico for rebuild.

You think it might make a difference what size the shop was and how many other alternators are in front of yours? Don't you think it would be best if you ask the people that are going to do the work? Don't you think?

Go to Rock Auto and buy a new or rebuilt one.At least you have a warranty.Also,depending on what parts this shop has to replace,it might be more expensive this way.