Ive had 6# boneless butts take 16 hours. Every one of those things is different. There are lots of factors. Ambient temp, pit temp, wind,
amount of marbeling in the meat.
I would start checking temps at the 10-12 hour mark and then every hour after that. I usually pull between 190° and 195°. If they're bone in, then they're done when the bone feels like you can just slide it right out.
Al