Advice on cooing larger brisket

Yesterday. JK, I assume you meant 3:00 tomorrow.:-D

The thickness of the brisket seems to play more into extra cook time vs overall weight. I've had a 19lb finish before a 14lb'er on the same cook. That being said it could take another hour+ maybe vs an 11-13lb. At home cooking 325-350 most brisket take me 6hrs and for a 21lb'er i'd give it 7hrs.

The time to fire up your smoker really depends on how long it takes to come to temp. I just say if I was cooking a 21lb'er and wanted to serve at 3pm, the meat would need to hit the pit around 7am to be done by 1-2pm'ish and rest for a bit. Starting smoker time again doesn't factor in since we don't know how long your takes to come to temp. Using my weed burner my pit comes to temp in a couple minutes.

Have fun. Take some pics of that monster!! :-D

That's a thick looking brisket. I haven't found at the hotter temps I cook that there is much change in time per pound. 275F is one hour, 300F is closer to 45 minutes, per pound

It might be 21 lbs in the package but you're gonna trim off at least 3 lbs of fat I'd guess about 7 hrs cook time + 2 hr rest so fire the pit at 5 am and meat on by 6