Even if it is for a dinner time meal the common estimate is 1 to 1 and 1/2 hours per pound. For 10 lb Boston butt that would equate to about 15 hours by my math. It's been my experience that for whatever reason every cut of meat I ever smoked ends up taking until the upper end of that window or longer.
Like I said it's a lot easier to have it end up done hours early and let it rest than it is to have it end up late and have everybody hungry and upset. all it takes is a couple situations where your smoke runs long and everybody has to wait an hour or two extra to eat and you start adjusting what time you start them. Since I wake up pretty early anyway I previously assumed it would be easier to just put it on first thing in the morning but what I quickly discovered was it's even easier to put it on before you go to bed the night before.
I didn't monitor anything throughout the night and when I rolled out of bed this morning it was exactly 165 degrees... Time to foil anyway. I preheated the oven to 225 foiled that bad boy up and brought it in for the rest of the cook which just finished an hour or so ago. Had I started it this morning I would have been well behind the eight-ball already.
I don't know who these superhumans are that are able to smoke a Boston butt in six or seven hours but that's never been my personal experience.