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Depends on what engine and what year vehicle. However, from your description of the coolant hoses, I'll assume the old style with the 3.8L (L36/L67). Not sure if GM sells just the pulley, without the entire tensioner assembly.
Easy to diagnose with a long screwdriver to listen to the pulley while the engine runs.
On one of those engines mentioned above, the generator has to be removed.
As for one-hour time. I know of no dealers who charge anything less than one-hour to perform any job. In fact, a lot of aftermarket shops charge a minimum of one-hour to do any job (unless it is an advertised job like tire rotation, oil change, etc.)
Even furnace repair charge a minimum of one-hour.