30 min, depending on your riding ability. Sport bikes can do it in less time, naturally.
I'd start from Deals Gap Motorcycle Resort, go to the end of the dragon, loop around and do it a second time (to make sure you get your photo taken from both directions...if you didn't know, they have pro photographers there taking pictures, and you can buy them online. Makes for a cool addition to your office or man cave).
Stop at the restaurant at Deals Gap MC Resort after your 2nd runb on the dragon and have a meal...but be prepared to wait a little while for your food.
Also, Best time to ride the dragon without the crowds is in the morning before 11am and later in the day after 5. If it's a holiday weekend, it may be packed and doesn't matter what time you get there. I hit it on 4th of July wknd last year, and there wasn't very many people. I went again for Labor Day wknd, and the place was PACKED. Driving the dragon was more of a chore, because there were too many bikes.