Multiple Butts Question

BamaEGG

So I've read on here that the rule of thumb is 1.5 to 2 hours per lb. Does this mean that a 16 lb pork shoulder would take 32 hours to cook?

Has anyone done this?

What about doing multiple Butts at once? Do you go by total weight or the weight of each butt? like does two 4lb butts go 16 hours or 8-12?

I have noticed that smaller butts seem to take longer than 2 hour rule.

thanks for the help.

Scott