On average I find a brisket takes me about 1 hour to 1 1/2 hours per pound in the 225 - 235 range. However, my smallest brisket has been 9 lbs. One of the greatest things I learned on this forum is the cooler/foil/towels trick. If I am cooking for a specific time I give myself a three hour window and employ the cooler/foil/towel trick. What I mean is I will start my smoke 3 hours before what I would expect to be normal. That gives me a chance to deal with long stalls, low temps, winds, rain, etc. When the meat is cooked to temp, I like to go to 195 for sliced brisket, I can double wrap it in heavy duty aluminum foil and put that in a cooler lined with cheap towels, then toss more towels on top of it, and close the lid on the cooler. It will keep for hours that way and I always make my deadline for serving.