I double down on what PadronMan said, you cook to internal meat temperature, not time. Each hunk of meat behaves differently. Two identical looking 8 pound pork shoulders, which are cooked at the same time, may be hours longer for one of the two. I smoked a 5.5 pound chicken last night, thought it was only going to take 3 hours, ended up taking 4.5 hours. Factors like these can make meal planning a bit tough. Pork Ribs are probably the most predictable. Cuts which are the same thickness, length and weight tend to finish at about the same time. I always plan on (worst case) 6 hours for ribs smoked at 225. Some times they finish faster, but usually that is more due to the thickness of the cut. My last 7 pound pork shoulder took 13 hours, even with 6 hours of it being wrapped in foil (the dreaded Texas cheat). Thickness of the meat "tends" to be one of the best predictors of time, but different cuts definitely take longer for a given thickness. And, every time you flap the door/lid to your smoker, extends the cooking time (if you are looking, you aren't cooking). This is why so many people here use remote thermometers, such as the Maverick ET-733. With an MES 30, consider getting the Amazingproducts.com A-Maze-N pellet tray smoker; you avoid having to feed the chip tray every 30-60 minutes this way. The tray, along with an external thermometer helps make smoking more "hands-free".
Good luck with your endeavors.