Lots of good advice above. One more key point. Unless you are experienced to the point that you can test doneness by touch, you need to use a quality instant read thermometer. Your target point temp is about 203 +/- 2-3 for pulled pork. Lots of articles out there about thermometers, but look for a Thermapen and you can't go wrong. Good luck on your pork butt. It is a tasty meat and a nice one to get started on. More forgiving than most other meats. A pork butt will take a lot of rub, more than a brisket. This is because there is less exposed outer area compared to the internal area. Lastly, I don't think I have ever a gotten a fulls size pork but off the cooker in less than 10-12 hours. But temp does affect the time. I like 250-275. Also, the size of your meat may vary, hence the necessity for the thermometer, as size dramatically effects time of cook.