In a hurry for ribs, but don't have 6 hours to wait? I gave up on the 3-2-1 method a few years back in favor of a modified version that has won several competitions.
Trust me when I say the ribs just flat out come out better; juicier, more tender (but not that fall-off-the-bone mush some people associate with ribs, I want to see a defined bite mark in mine, and not have the whole chunk of meat come sliding off the bone when I eat mine), and most importantly, in HALF the time.
I do mine on a knock-off Big Green Egg XL (thanks VID from a few years ago with the recommendation for the BBE from Aldi's; I literally only fire up the big pit when I need to do more than 6 or 7 racks), but the recipe should be fine as long as the heat is indirect.
I get my lump, red-oak charcoal rolling and stable to 325 F (Maybe 20-30 mins) while I trim, de-membrane, and season the ribs (either spare, St. Louis, or Baby Backs). I throw on a couple chunks of cherry (or whatever you like) on the charcoal, load the offset plate, then re-stabilize the smoker until there isn't heavy clouds of smoke pouring out, but rather "wisps". I load the ribs on after they have sat in the fridge for the rub to set, and set a timer for 1.5 hours.
If you go a little over 1.5 hours you'll be fine, but try not to pull them early. The first hour and half is when the ribs absorb the smoke for flavor, sets the rub to a nice bark that doesn't rub off when touched, gets the much loved-but-not-important "smoke ring" in the meat, and gets some of that yummy fat rendered. The 325 temp is pretty important, try not to go below it, or much over 350, as the rub will get too dark.
After the hour and a half, I wrap mine in heavy duty foil. You can add any number of braising liquids at this point (apple juice, honey, butter, etc.), but I skip all of that, and just wrap the ribs to let them finish in their own juices. After they are wrapped tight, throw them back on the smoker for about an hour. After the hour long braise, I'll poke through the foil with a temp probe or a tooth pick; if it slides in like butter, your ribs are almost done! If you HAVE to have them be "fall off the bone", braise them for 1.5 hours. DO NOT GO ANY LONGER, or they will literally be mush, and will fall apart when you try to put them back on the smoker for the final step.
Finally, I unwrap the ribs (reserving the juice in the foil), pop them back on the smoker, brush them down with your favorite sauce and the reserved juices, and let them go for another 15-20 minutes, until the sauce is set. (you can speed this up, and add a little more caramelization by turning the smoker up to 350/375 while you are unwrapping them from their hour long braise.)
Voila! You now have perfectly cooked ribs, in HALF the time. Try it some time, it really does work, and I'll never go back to 3-2-1.
Cheers all!