Agree mostly with above, but more conservative in estimate. I'm a self declared auto DIYer and have done lots of projects on my GN over the years including PMs, baer disks, drums, lines, etc. I spent a lot of time reading the forums and gathering information to include the steps on the gnttype site. Also picking my components and procuring them. Researching and buying proper paints for booster and cylinder and prepping and painting those parts before install. I live in a 'small town' and I had a hard time finding vac lines to replace the ones on my vacuum block that looked suspect when I switched the block out. (not technically part of the brake conversion...but additional self imposed tasks). Bleeding the cylinder is easy with the right bleeder tool.
The actual install is not too too bad. But I'm 5' 10', 160lbs....I can't imaging a big muscular weight lifter guy doing it - I had a hard time maneuvering under the dash to get the brake pedal work done (nuts on an off, pedal installed/aligned, etc). one of the mounting bolts for the PM assembly (now the booster assembly) had a 'push nut' on it in addition to the regular nut...that was a pita to get off. Also spent some time cleaning and 'arranging' the myriad of lines that traverse the area where the booster mounts to the firewall. I also bled my brakes after final assembly because I wasn't sure or confident I could "get the bubble out where the lines connect to the master" as mentioned above. I sometimes overkill my thoroughness. New/clean brake fluid can't hurt anyway. Oh yeah, my brake light switch needed to be adjusted after all the work in that area (small task).
If everything would have been lined up ready to go, sure 2-3 hours labor...but in reality, took me two Saturdays of about 4 hours each on car...and then all the prep work I described.
piece of cake ;-)
good luck