The question is what is your state of conditioning and what is your experience in hiking in generally dry and arid southwestern US conditions? Only you know the answer. If you are not familiar with the climate, i would definitely start out easy. Get a campground permit and take two days. It will be a lot more enjoyable.
https://www.nps.gov/grca/planyourvisit/hiking-faq.htm I assume you looked at this website. I note that the NPS does not recommend hiking to the river and back in one day. It certainly has been done, but lots of people have called for a mule ride back out of the canyon, which is a thriving business for the concessionaire.
The Canyon is neat country with everything from easy to extremely difficult excursions possible. Take your time and get acquainted with it over time. Grand Canyon isn't going anyplace....
Whatever you decide to do, I hope you have a good experience and enjoy your time there. Incidentally, the desert southwest has many, many fascinating localities. GC is just the tip of the iceberg.
one or more gifts or other benefits from the co-op.