An hour? But, I'm easily entertained by my devices and probably wouldn't notice the time going by. It also heavily depends on what else I have going on; I always pad my schedule for doctors, but even so, there might be something else I have to get to.

It's medical. The person before me may have needed more time. I think doctors have a harder time than most estimating how much time a patient will need, and I don't want them rushing me out the door.