Depends on the horse, what it's level of training is, and what job I have to accomplish that day.
First ride on a colt? Fifteen minutes is long, although I might put an hour in sacking it out with the rope and saddling the first time.
First thirty days on a colt? 45-90 minutes, although it might go longer if I have a fence to ride that needs work. That can be an all day ride, albeit at a walk with lots of stops.
Branding? Maybe twenty or thirty minutes for a green colt, four or five hourse for an experienced working horse.
Gathering cows off the mountain? Ten or fifteen hours is not unheard of.....