What are the cuts? Points? Flats? Both? Are they separated or not? One piece, 2 or 4?
Generally for a packer brisket, you're looking at between 11-15 hours cook time if you maintain 225-250* in the cook chamber. Smaller pieces cook faster. It's not really about time; it's about meat temp. "It's done when it's done" is the motto around the smoker. Your 2 main temp goals are:
165* -- smoke until you hit this mark, then foil (you will hit a plateau or "stall" -- wait it out & don't panic. The connective tissues are breaking down.)
195-205* for slicing or pulling.