I really like this breakdown of what one has to do. For my little laptop-selling side business, I have the install-and-setup process pretty heavily streamlined, and it still takes time to do things like get all the relevant driver updates installed and test the machine to ensure it's fit for sale. Probably around an hour or two per machine, but with a lot more downtime than this process involves.

I would generally advise against buying an HP in this day and age, though.