Most times, it seems to take 10-14 hours to smoke one of these for me (depends on the size and temperature you want to use)...and this one was a good size so I expected 14 hours. I didn't feel like getting up at 3am to get the smoker up to temperature and stable which is why I threw it on last night since I had to stay up til after midnight for work anyhow. After I take it off the smoker, I usually wrap it up and let it sit anywhere from 30min-1 hour which seems fine to me.
I have wrapped them in foil, towels and put them in a cooler many times though and have kept them for up to 6 hours without a problem and can't tell any difference vs. when I let them sit for 30 min. You almost can't screw up a boston butt pork shoulder. It's pretty fool proof.
I was thinking 30 minutes was the bare minimum. 6 hours seems like it'd be amazing...