I know all Jeeps are different, but my RMS install took 10 hours. Sure, some of that time was spent driving to NAPA to buy a second rear main seal because I dorked up the first one during the install, as well as two hours cleaning the lower bearing cap, but it still took that long from start to finish.
I used four or five different sets of instructions I found on the forum because I was not completely happy with any of them, 5-90's included. I took my time and felt I did a great job, but my seal leaked for about a week after the job. Seems to be holding up now after swaping the OFA o-rings a few days later.
X2 on what others say about the OFA o-rings. I'm thinking that I had so much oil under my engine from the leaking OFA, that my RMS was good and not in fact leaking. I have no way of knowing that now but suggest starting with the $8 OFA o-ring swap first and see where that takes you. That job takes less than 30 minutes.
When and if you do the RMS, make sure you get the right RTV and use the right amount.
Edit: I re-read 5-90's instructions and have no problem with it. I just like pictures and I found several instructions that supplemented his write-up.
One thing I did find helpful that 5-90 did not mention is the use of rubber bands to hold the oil pan gasket in place during install. He suggests using studs, but four rubber bands can be used to hold the gasket in place very effectively. Loop the band through the hole and back through itself, and pull tight. You'll see. Once a few bolts are installed, you can easily remove the rubber bands. See, pictures would be helpful.