Hey, I have done a single brisket on my 18.5" Weber smokey mountain a couple of times and it always comes out great. Usually takes about 15 hours for a 13lb brisket.... For an office party I need to make TWO briskets... what do you think the cooking time will be? If one took 15 hours do you think two will take 18-20 hours? More?!?! Gotta get the timing right! Thanks!