Kirk - drive is easily doable in a day - about 750 miles...from South OC. I've done the drive into Grand Junction from here a couple of times - 800 miles. Always iron butt it home on Sunday. Try to get out of Moab at 5 or 6 am to beat at least some of the Vegas traffic home. Still sucks when you hit the PRK border and towing a trailer, I'm stuck with the trucks!
I did the drive in October only we went through Zion on the way to Moab. Right now I am planning to Leave SoCal early morning Tuesday and depart early Sunday to head back home. I have Wed daytime free and Saturday all day free for side treks based on the runs I signed up for.
The drive from Zion to Moab sucks in the dark fyi. Poorly light two lane roads in thick deer country.