It's exactly 53.2 miles.
Onion Creek @ Mile 85 (that's 85 miles above the confluence of the green and colorado) in Professor Valley, on the Moab Daily is one of the better camps on the stretch. Also Hittle Bottom @ Mile 88 is a nice camp with toilets
No Dams until Glen Canyon (Reservoir [Lake] Powell)
3 Days = haulin'
5 Days = leisure
These are low water estimates and are on the conservative side.
You should probably pick up a copy of Belknap's Waterproof Canyonlands River Guide. It's the essential companion. Here is a link:
Amazon.com: Belknap's Revised Waterproof Canyonlands River Guide (9780916370114): Bill Belknap, Buzz Belknap, Loie Belknap Evans: Books
Practice Stewardship, Enjoy.