Everything I've read says smoking pork butts takes 1-2 hours/pound. I have never experienced that kind of range until last weekend. The final cooking time for butts has always been within an hour of 1 hour/lb. Last weekend, mild day, smoker at 225 deg, my 7 lb butt took 14 hours to hit 195 deg. I didn't try to rush it and it may have been one of the best. Luckily, we didn't have company waiting for dinner! Give yourself plenty of cushion if you have time constraints!