Yep, guidelines, ballpark, WAG, estimated, average and other synonyms.
A 5lb butt cooked between 225°-300° can take anywhere from 8-14 hours.
Inject it and it can take 12 plus hours.
Had a 9lb injected butt take 19hrs.
I did four butts the other week, three finished right about the same time, but the biggest one finished a good hour or more before the others.
Each hunk of meat can be very different due to so many variables.
I've two butts going in the smoker tonight, one is approx 6.25lbs and the other 8lbs.
They'll be done whenever they probe tender and no sooner.
Tenderness is everything, internal temp is a guideline and cooking time is simply noted after the cook.