A rough guesstimate would be about 7 or 8 hours. You normally figure about 1.5 hours per pound, including the rest.
I smoke my brisket in a pan sitting it's own juices. After trimming the fat off I put the fat on a rack above the brisket so as it renders it will drip on & baste the brisket as it cooks. You can cover the pan with foil around 165-170 IT & it will shorten the cook time. Cook it to an IT of 200-205 or until a toothpick goes in with no resistance, like room temp butter. Keep foil cover on & rest for 1/2 to 1 hour on the counter. Then slice. You can use the pan juice to make an au jus. Here is an au jus recipe from Chef Jimmy J
ChefJimmy’s Au Jus
1- Lg Onion,
3-4 Ribs Celery
3-4 Peeled Cloves of Garlic
Toss them in a pan under the Beef, and let the whole deal Smoke for one hour,
THEN add 4-6 Cups Beef Broth,
2 Tbs Tomato Paste,
1/2tsp Dry Thyme (4-5 sprigs Fresh)
1-2 ea Bayleaf
Finish the Smoking process to the IT you want.
While the Roast is resting, dump the pan juices veggies and all into a 2-3Qt Sauce pot and add 1Cup Red Wine, something you like to drink, and bring the Jus to a boil, lower the heat and simmer 20-30 minutes. Strain out the veggies and let the Jus rest a minute or so for the Fat to rise. Skim off the bulk of the fat then using strips of paper towel laid on top of the Jus then quickly removed, take off the last little bit of fat.
The purpose of Smoking the Vegetable for 1 hour before adding the Broth and Herbs is...The Smoked vegetables Roast in the Dry heat concentrating their Flavors and Sweetness giving the finished Jus a Richer, Deeper, Full Flavor.
Serve the sliced Beef Au Jus or thicken the Jus to make Gravy
Hope this helps