Serpentine belt, how long will it take to replace it?

Depends on what caused the belt to be damaged. That rarely happens on its own. There is two belts on your engine. The larger one calls for 0.5 hours to replace, which suggests it is not an easy job. You must add another 0.2 hours if the AC compressor belt must be removed.

These times do not include inspecting the pulleys, mainly the idler pulleys, to find what caused the belt to run off-center and be damaged. If the cause is not found and corrected, the new belt will do the same thing.