I wrote about this a year and a half ago and I want to encourage you to try it.  It gets better every time I make it.

Smoking a brisket is not like baking a cake.  It is not exact. The constant is, bring the internal temperature of the meat to about 160 °F.  The meat will be succulent, caramelized and very dark on the outside, a red smoked ring and then juicy meat to be sliced thin across the grain to eat plain or put in a killer sandwich.

There are so many variables, the style of your smoker, the size of the brisket, the temperature and weather of the day and on and on.  Pick a brisket that is whole, thick and with  1/4 to 1/2 inch of white fat on the top side.  Do not use a super trimmed brisket, the fat needs to drip and will keep the meat moist.  It takes all day, about 8 to 10 hours to smoke a whole brisket.  I started in the morning, placed the brisket on the smoker at 11 AM and we ate dinner at 8 PM.    Adjust your start time to earlier in the day for early dinner.