My friend and I took care of mine in about 12 hours across 2 days. At that point, we'd never done a BL before, although we both knew our way around the tool box and a knew fair amount about cars/trucks.
You should really budget for 2 days on the 3". It would REALLY be pushing it at 6 hours, even with a crack team, especially if you have an auto. I didn't have to extend my t-case or tranny shifters on my manual, but from what I've heard, you DO have to on an auto, which means welding in an extension.
It's been a few years, but if you have any questions, feel free to post them up and I'll see what I can do to dig up the answers.
Be sure to start hitting all of your body bolts and ESPECIALLY the steering shaft knuckle with some PB blaster weeks before you plan the install, this will save your knuckles and a lot of aggravation. It took us 3 hours to separate the steering shaft because of the rust (granted I was out of MAP gas at the time).
Here's the thread from my install:
http://www.nexterra.org/forum/viewtopic ... ght=#18768
Check out the additional photos from the install:
http://s5.photobucket.com/albums/y167/f ... ra%20Lift/
There are plenty of good pictures in there that show things that the instructions DON'T cover (imagine that), like the notches that have to be cut in the rear bumper after it is relocated to clear the frame horns and hitch.