Well, for many, many years, when briskets were big and had a lot of fat, I preferred to smoke my briskets at least 24 hours. That was easy, I usually had a 14 lb'ers and smoked it at about 180 for a long time.
The smokers I was using, various offsets, were better suited to that cook.
As the meat changes, leaner actually, I found that I could do as well with 12 hour cooks and get almost the same effect.
Those long cooks need a lot of fat to protect the brisket...but in the end, you had this beautiful piece of meat that looked like a meteorite, which was how we defined briskets back this.
I think it's just a function, that meat changed, and I didn't like tending fires that long, that change my method to more like 225 to 250 for temps.
And there are some out there who like express cooks for their briskets, cooking over 300, but I've never like those results.
Smokin