We did not do it in a day but it took us exactly 3 hours to go from the top of the South Kaibab trail to the river (with big packs on), and the next day exactly 6 hours to go up the Bright Angel trail from the campground to the top. So, 9 hours total but all in one day? Uff, I know folks do it, but wow.

The worst part was near the top of the Bright Angel coming up you start getting into the hordes who are just coming down the trail for a bit, and we had 50# packs on, and had been hiking 5+ hours up. I actually had to tell a dude to stop carving his name into the canyon wall at one point, but judging by the blank look he gave me, he didn't speak Engligh.