I got charged 8 hours to install headers and replace the entire diff with a separate unit. And installing the headers was not that easy.
In order to replace the diff, I am told you need to drop the exhaust. I would think 3-4 hours real time would be enough. The diff itself shouldn't be that bad, assuming a floor jack to remove the old one and lift the new one in place
its extremely simple. I dropped my exhaust because i put a new clutch/tranny in but i do not think you will need to.
3 bolts I believe 18mm that hold the diff in place. The passenger side rear bolt is hard to get to so i used an 18mm socket and a pair of vice gris to hold it. It came right off.
there is 8 driveshaft nuts i believe 15mm or 16mm and you will need inverted torx for the axle shafts.
the easiest way to do it is put the ebrake on and loosen as many driveshaft and axle bolts as possible, the release the e brake and turn the tires. apply the e-brake and loosen the rest. then just remove the three diff bolts and your out