I do my pork shoulders sort of like Naaman does briskets. Dry rub, cook till ~150ish internal, wrap (I add apple juice to the foil), cook for a few hours that way till the internal gets pretty high but no real target, and then unwrap and cook until it hits 200. The rub I use is brown sugar, salt, pepper, cumin, garlic. I did a 4lb shoulder last weekend and it took a solid 9 hours and probably could have gone longer. It still pulled ok, and tasted great, but I let it go too long before i wrapped it.
Basically I'd budget around 2hours per pound, to be conservative. More if the but is partially frozen like mine was.