Allow 2 hours per pound, but use that as just a guideline, the real timeline is "when it's done, it's done!"....As Smoky pointed out, it comes down to numerous factors, the piece of meat itself, the smoker you are running, the temp you are cooking at, and on and on....Typically, the higher the grade of meat, the faster it will cook, this is due to the internal fat content or marbling being higher than in a lower grade of meat. When I cook primes for comps, they tend to finish about a half hour to an hour earlier than a Choice or Select. My pit is a reverse flow stick burner, I will typically cook a 12-15 pound brisket to toothpick tender in 7 1/2 to 8 1/2 hours at 250 degrees. Once the meats IT reaches 200, start checking the flat section for tenderness, once a toothpick slides in easily, it;'s done, pull it, wrap it up in towels and off to a cooler until you're ready to slice and serve. I never want to pull a brisket off the pit and head straight to a cutting board, I prefer at l;east a 4 hour rest, with no less than 2. The IT really needs to come back down into the 160's before you slice into it. I rub mine down 1 hour before I plan on putting it on the pit (usually right before I start my fire), then back to the fridge. Get my pit temp at a steady 250 (235-265 range), then the meat goes on fat side down, for 4 hours with a mix of Hickory and Oak woods, then at the 4 hour mark, it's wrapped in a foil pan with either a cup of broth or reserve au jus from a previous cook. Good luck with your smoke!