Definitely no more than 10 minutes. This includes taking the used one off, clean up, apply lotion and letting it completely soak in before applying powder and putting on a fresh diaper.
About a minute or two depending on if its a diaper brand I use often enough to know exactly where the tapes should be or not.
Maybe a bit longer if using cloth since getting the snappies in the right place is a bit more work, tucking the legs in and getting plastic pants in top etc. Still no more than about 3 minutes though.