For guesstimation I ballpark 1 1/2 hours per pound. But.... you have to consider the ambient, the smoker, the heat, type of smoke, rub, etc etc..... I am about to put on a 14# brisket, box is hot, trying new A-Maz-N 3x5, in a MES30. Going to get it to 230, stick in the meat, light the smoke generator, give it 30 mins. check it, and 30 mins again recheck ( I should have been a safety engineer belt and galluses). If it looks happy happy and the smoke is percolating real pretty, I am going to forget it till in the morning and then stick it the with a thermeter just so I have an idea if it enjoys itself tonight. Then I'll know how to proceed.
Best way to do brisket is to get it the way you like it, then see if a toothpick encounters resistance. If it is smooth in and out, bag it and tag it and let it set at least 1 hour but 2 is better.
Smoke at 230, IT to 180 to 190, bag and tag to rest in the ice chest ( the one without the beer), and enjoy it a couple of hours later when the wife gets all her stuffies done. Me, its just brisket, bread, onions, and cold beer.... I don't wanta to be a pig.....LOL
Don't forget to take a second today and remember those who sacrificed so we could enjoy it.
Oh, thats a nice lookin brisket ya got there.