You can probably do the lower canyons in three days...
You probably could, just watch for the wall bangers. Prehistoric river currents have created deep undercuts where the river suddenly turns and the current tends to push you straight into them.
But what's the point? In my experience, any wilderness experience should not be rushed. It takes me 2 days to shed all the mental baggage of where I was, before I can be totally where I am. And the last two days are full of thoughts about what's next after the trip; what I need to do when I get out to the world, and sadness about leaving. It's the days in the middle where the blessings are. To me the whole point of this wilderness/solitude thing is to get away from the world and live entirely in the present; to manage the next turn or ridge, where's the next water, food, camp, critters; to be a part of the moment in the place. Its mentally and spiritually cleansing. "If you ain't where you're at, you ain't nowhere."
The Lower Canyons are great for this. You're essentially cut off from the world. You have to be where you are to get to where you're going; to rush to the end is to lose the whole point of the experience. It's a zen thing: paradise is in the task, not the goal. spc