Why wouldn't you have the time? If you started with it on your shoulder, would you have the time to bring it down to your hip? Maybe I'm being a little cranky today but where are you people getting this stuff? Shotguns that don't have to be aimed? Shooting from the hip? Racking the slide when confronting possibly armed assailants? What's next? Advocating the Linda Hamilton one handed chambering?
Shotguns have been known to have been grabbed and taken away from cops and home defenders alike when shouldered or carried above the waist.
Having the shotgun at waist level works to the cop's or defender's advantage. Making it much harder to deflect, snatch or grab away.
There was a well publicized instance in Olney, MD where a single mom deterred home invaders after calling the cops. By loudly announcing her intentions to defend her home and daughter.
Then hitting the Bolt Actuator of her BushMaster 5.56 carbine. The home invaders heard the loud sound and fled the home and property.
Jack.