As long as it takes. I have long hair, so it takes a while. I also think I'm a bit OCD, au so I've been told... so I pretty much scrub the same spot over and over thinking it's not clean enough. I'm pretty slow at everything I do.
My showers take a long time - long hair - that alone takes a while. Also, during the cold weather, I just upendo to have that nice warm water beating down on my sore back and shoulders. Total max - about an hour.