That size,was often cut from the flat on a very poor old dairy cow,that nice little ladies in New England use to make yankee pot roast.
Use plenty of carrots,potatoes,etc.
First advice Smokin' would give is,"never cook the first one for company".
Yes,8 hrs should complete the entire process.
The next piece of advice,I really HATE.
That said,cook it at 225*-250* until 160* internal-MAYBE 2.5-3 hrs.
Paint it heavily with a red bbq sauce[maybe 4 oz] and a couple TBSP of wooster sauce,and double foil.
Cook at 250*-275* until close to 195*,wrap in a heavy towel and let set 2 hrs.
Tell the guests that for true COWBOY brisket,everyone drinks at least three Shiner Bock,or comparable southwestern style beer and at least three ,two oz shots,of cheap Tequila,with lemon and salt,for authenticity.
Slice across the grain,ladle some of the drippin's over the slices,pass some chopped jalapenos and onions
Sides of pinto beans,a spoonful of tater salad,and some sweet cornbread.
Play some Jerry Jeff Walker,or Asleep At The Wheel
Shoot a sixshooter in the air,when they try to drive out the drive.
You will go down in your neighborhood folklore,as "the man" for cowboy cookin'.