A friend and I did this trip a few years back. The shuttle ride was long (especially after driving from LA earlier in the day). The hike down from the North Rim is beautiful, but seems to go on forever. The signage is very poor so you have no idea how close you are to the bottom. I don't know what time of the year you were planning on doing this, we did it at the end of May and it was 126 degrees down at Phantom Ranch. Needless to say, we spent most of our rest day sitting in a shady part of the river relaxing. Just get an early start (like 5am) for your hike back up to the South Rim.