Can a patient be in coma for less than 6hrs (as 6hrs is minimum)? what's the diagnose that someone is in coma?

A coma is a: Prolonged state of unconsciousness, during which a person is unresponsive to his or her environment, is alive and appears to be sleeping, but, unlike being in a deep sleep, the person cannot be awakened by any stimulation, including pain. I do not think there is a minimum time frame but, according to www.Brainandspinalcord.Org, a coma can last for a few seconds, or can last for years.