Just for reference, the last packer brisket I did was 13.6 lbs.(package weight).. Trimmed it down to 10.5 lbs.Finished weight after the cook was 6.5 lbs. Total cook time was16 hrs.@ 225-260 +/- Probably could have been done sooner, but I had some firebox issues and lost some time.
If you want to serve it at 6PM Christmas day. I would give yourself plenty of time and start it the night before around 9 or 10 pm and it should finish around noon Christmas day. Put in cooler packed with bath towels and hold till your ready to eat at 6PM.It will still be plenty warm. May need to just put in the oven to reheat a little before serving. OR....
Cook it a full day or two ahead. Give it a good rest packed in cooler(up to 8 hrs or longer) , slice and put in vacuum bags and refrigerate. Place bags in boiling water to reheat and serve.Or put slices in covered foil pan with some liquid and reheat. Nobody will know the difference and it will be great.(My best briskets are always the ones I let rest the longest in a cooler or warmer)
Also, finishing in the oven is done all the time. After your done smoking and wrap in foil, all that's need at that point is a constant heat source to finish cooking. Makes no difference if it's in an oven or your smoker/cooker. heat is heat. Make it easy on yourself.
For a rub, mixture of 50/50 kosher salt and course black pepper. For your first one keep it simple and don't try to over engineer/over think things and it will be great. Good luck!
