I do a lot of grilling but I am a novice at smoking. I decided I would smoke a brisket for Xmas dinner and thought I was ordering a flat brisket because estimated weight was 8-10 lbs, but when I got the order home I discovered I had a 20 1/2 lb packer brisket

. I still plan on going through with smoked brisket for Xmas dinner. I'm a big fan of using brines when I smoke or grill, so I plan on letting it soak in an apple cider brine for a couple days. I'm worried about the timing. The temperature here will be below freezing, so I think I should allow at least 24 hours to cook.
Does anyone have any tips or advice about time, temperature, or preparation of brisket?