The itinerary for the third day of this trip is as follows:
8:00 Depart from the hotel
10:00 Those who are not flying will be taken to the Grand Canyon Vistors Centre where you are able to access all free bus services and can fully explore the entire south rim.
10:15 Helicopter flight time
15:00 Depart the Grand Canyon and continue with your tour over to the Desert View and pass the Painted Desert, Hopi & Navajo Indian Reservations & the Little Colorado River.
That sounds pretty much the same itinerary as I experienced when I went on the Yosemite/Classic California trip back in September.
I did the fixed wing flight rather than the helicopter. From memory, when the coach first arrived in the Grand Canyon resort area it dropped a group of us off at the airport, including myself, then continued on and dropped off the helicopter group somewhere else, and then dropped the remainder of the party (ie those who weren't flying) at the visitor centre.
We had a bit of a wait to get on our fixed wing plane, then we were up in the air for 45mins I think. After we landed we waited in the airport for about 10mins or so before the coach returned to pick us up, and it took us the short distance to the visitor centre where we found most of the rest of the group still were. So in fact I ended up exploring the canyon with others who hadn't done either of the flights and I didn't feel I'd lost precious time.
You're given maps which show the routes of the hop-on-hop-off tour buses which take visitors around the canyon, they're very frequent and are free, so you can easily get to see plenty of the canyon in the time you are there. I think if you wanted to walk the whole route you might be a bit pushed for time, but it's rather hot for that sort of thing anyway. Remember to drink plenty of water (there are places there where you can refill water bottles).
I found the Grand Canyon amazing... Fully deserving of its great reputation. When you get there and look across it, the scene before you is just so vast, calm and beautiful that it feels more like you're looking at a painting than real life.
You're in for a fantastic holiday!
Dave