I smoked my should last weekend and it turned out awesome, here's what I did.
Saturday morning I opened the package from Costco and found out that the 15 lb shoulder had already been cut into 2 smaller pieces. Took both pieces coated them with mustard then a good coating of my rub. Wrapped the them in a double layer of plastic and put them in the refrigerator this was about 8am.
At 1pm I started my smoker with 2 chimneys of lump charcoal, and a couple of small logs of oak & apple. I have an unmodified Char Griller offset firebox smoker, so I place a pan of water on the charcoal grate in the main chamber as close to the firebox as possible, I think you can see it in the one photo.
At 2pm I put the meat on the grates and closed the lid. I checked the charcoal/wood level about every 2 hours and added charcoal and wood as needed. I was using a combo of Oak, Cherry, Apple & Hickory. At around 6pm I flipped the meat and inserted a temp probe.
I continued to check the charcoal/wood until about midnight at which point I took the meat off the smoker and put both pieces in a foil pan. I added about a 1/4 apple juice and covered that with foil. At this point the internal temp was reading 142 degrees. Here's where I cheated a little bit, I put the covered pan in the oven at 200 degrees overnight, I needed a good nights sleep.
Sunday morning 8am I got the smoker going and removed the pan from the oven. I placed the uncovered pan back in the smoker. At this point the internal temp had made it to 190 degrees.
I tended the smoke the same as the day before, adding charcoal and wood as needed. The highest temp I saw on the pork was 195. The smoker temp gauge never went above 150, I don't think the supplied gauge is reliable.
At 3:30 I pulled the pan of meat off the smoker, covered it in foil and let it rest till 4:30. I then attempted to lift it out of the pan to pull it but it just fell apart in my hands.
Here's the finished product.
So I guess my total smoke time was 25.5 hours. I think I could have probably cut that by a few hours but I don't think the extra time hurt the pork at all, probably because it spent the night covered in the oven.