I cooked 14 packer briskets today for less than 8 hours at around 260. Most were only around 190 when taken off (they're in the walk-in cooler to slice tomorrow, add some juices and heat in the oven for a luncheon. Weird stuff that a smoker full of packers was nearly done in less than 8 hours. It just depends on the meat too. These were select grade (not MY choice to order!) so maybe that had something to do with it. Get a feel for what's "done" by pushing on your brisket. Also, slide a probe it... when there's no resistance, it's done. Takes practice.
KCBS Member #14287