I'm a total newbie and have done 2 butts 6lbs at 225 took 15 hours to reach 190...Did a 2nd 9lbs took 19 hours. I peeked and sprayed with apple juice/cider vinegar 2 times. Everyone loved them. My observations that might help you were.
1. I started with a pretty small chunk of wood (the size of two golf balls), I don't know the weight but seemed smaller than the recommended 4-6 oz. I did this cuz several prior posters stated their first attempts were black and to smoking. Maybe that's a rookie mistake or a taste thing, some people like it super smokey others like a mild smoke flavor.
2. The "plateau" period...It can be a bit scary when you are monitoring it... it goes up in temp pretty steady up to about 160-165 then it just plain crawls up to 170-175. You can start to panic cuz it feels like something is wrong and its not going to finish in time for guests. So I would totally recommend starting the night before to guarantee it's done in time.
3. When its done and you open the door you might panic a bit with how dark the bark is...As a open flame BBQ griller it looks like you killed it (burnt)...But when you pull it and put it in a big platter and season with Smokin's finish vinegar base sauce...It tastes AWESOME!!!
Good luck and GO NINERS!!!!!!!