.....''The length of time that a person is knocked out for typically depends on the severity of the traumatic brain injury.According to Headway,if someone is unconscious for less than 15 minutes,their traumatic brain injury is considered mild.A loss of consciousness between 15 minutes and six hours is considered a moderate traumatic brain injury,and between six hours and 48 hours is severe traumatic brain injury.''
So you can be knocked out for any length of time really!