[ChiefGator]

Depends on the temperature you smoke it at... some good BBQ chefs like to smoke a brisket at a higher temperature. Aaron Franklin smokes his at 275 degrees, for exampe. In that case, it shouldn't take more than 12 hours to smoke it, especially if you get it out and let it rest at room temperature for a couple hours first. And, don't forget you need to let it rest at the end for at least one hour as well.

I think sixteen hours including final rest is more than enough if you cook it at 250-275.

I have cooked large wagyu briskets (14-16 lbs) around 250-275 and it usually is done within 12-14 hours.