Mans back
Laser hair removal times depend on which laser you are being treated with, how good the laser operator is, and the area being treated. Using a fast and almost painless laser like the LightSheer Duet (which has the new very large hand piece), a man's back would take 20-30minutes.
A full back can take anywhere from 20-40 minutes depending on the size of the back, the type of laser, and whether or not you are including the shoulders too.