I'm doing my first smoke on a digital 6-rack. If I am going to smoke an 8-pound pork butt for 12 hours but the oven timer only goes to 9:40, do I just add more time later as it counts down to equal 12 hours? Same for the smoker timer.
Yes you will have to adjust. It sounds like you want to apply smoke for more than that. I usually only put 4 hours of smoke to my butts. They say anything more than 4 hours usually does not add much smoke flavor to it.
I've heard the same thing from people at the competition smokeouts. Any smoke beyond about 3-4 hours is mostly just wasting pucks. The meat is too done to absorb much smoke by then.
Though 12 hours of smoke is a lot. There is another school of thought the includes both smoke absorption, and smoke adhesion. Though smoke will only penetrate the surface of the meat until the surface gets to around 140°F and higher, and usually no deeper than a 1/4"; smoke will continue to collect and bond to the surface of the meat; as long as the surface is still moist. Still most generally apply around 4 hours for butts.