I have not done your exact route, but I have been on the "river route" several times in other parts of the canyon.
I think doing it a day might prove to be very ambitious. I don't know you at all, though, and you might be perfectly capable... that said, there will be many challenges, among them:
- Water. Although you're hiking "next to the river", sometimes you will be a thousand or so feet above it, with no easy/safe way to get down, so it will often be necessary to carry quite a lot of water with you, especially because of...
- The Heat. October is a great month to do GC, but daytime highs near the river can often be in the high 80s-mid 90s, and the sun is HOT.
- River miles vs. hiking miles -- add about 20-30% more miles because of detours around side canyons along the way.
- Tamarisk trees and prickly stuff. This varies from year to year, but in some places around the Nankoweap Delta, the tamarisks can be pretty nasty to bushwhack through. It won't stop you, but it just takes extra time/effort (which means more water needed).
Whether you take one day or two, I'm sure it'll be a VERY memorable trip!