That's about how long it takes, including photo stops and lunch, to work your way through Grand Teton and then loop around Yellowstone, clockwise. We were up at 4:30. No coffee until we hit Signal Mountain around 7:00. Actually, make that exactly 7:00. We arrived as the store clerk did. But the morning hours are worth it, being out before the day's gotten too old, you get better light (unless you're lucky and storm rolls in) and a better shot at seeing critters.
And the early legwork did pay off for those shots at Jenny Lake. They're included in the gallery below which is what the 15 hours on the road netted. It was a good trip. Saw a lot, but it still felt a bit like a rushed greatest hits tour.
Maybe go back one day and spend a bit more time in Yellowstone.
09 March 2013 Edit: With the site move, all of the shots from this trip are right here.