12 to 72 hours. Most people come down with it fairly quickly. Did you dad shut himself off from the world while he was sick? You may not have come across it at all. If he has his own bathroom, there's a good chance he hasn't spread it around. My hubby has had noro and never even told me - didn't have to because he has his own bathroom and took care of himself. And no one else got it or even knew he had it.