jcoop09,
Brisket isn't that expensive of a cut. So, pick up a couple and cook them both. Keep a knife near by and after a couple of hours on the smoker start to cut on one of them. This way you can see how time will effect the way the meat cooks. After a few tries you will figure out how you like it. Let some friends taste it and they will also tell you. Since Brisket is a cut of beef it can be eaten at a lower temp so you don't have to worry about bringing to a specific temp like pork.
I usually cook it at 220 for 6 to 8 hours or so and then wrap it in foil for a couple more. Like I said before, it just takes practice and practice is a good excuse to fire up that cooker! I have never had anyone complain to me when I tell them I am going to practice this weekend.
jcoop09, I might be mistaken, but after a couple of hours cut them with a knife? A person could also stick a temp probe (around the 4 hour mark to make sure it is out of the danger zone) in it instead of a knife. A brisket will get done by temp rather than by time.