The USDA Prime briskets at Costco are excellent. You will want to trim off the really thick parts of fat, but don't over-trim!
I temp both the flat and the point, and my ideals are 195 in the flat, and 200 in the point. Those are my minimums. I have found that 190 is not as jiggly and tender as I like. When your temps are there, check it and see if it's "jiggly", floppy, and bends easily (you will get to know this texture the more briskets you do). If so, it's ready for a rest in a cooler (double wrap in foil, and surrounded by towels. I try to rest at least 2 hours, and up to 6 hours is fine.
I often hear about brisket flats being dry when people do their FIRST brisket. This almost never comes from cooking to too HIGH of temp. The reasons in reality are 1) bought a flat-only cut from the supermarket which was overtrimmed and probably USDA "Select" quality (try to buy AT LEAST UDSA Choice, with USDA Prime, whole packer brisket the best). 2) Did not allow enough time, and rushed the cooking by turning the smoker to 250 or higher, which will make the meat "tense up" and render/squeeze out fat and moisture before connective tissue has fully converted to gelatin. 3) Did not allow enough time, and just pulled from the smoker at too low of internal temperature. Sometimes what our senses interpret as "dry" is really just a tough cut of meat that hasn't been allowed enough time/temperature to become tender. 4) Did not allow enough time, and did not rest long enough, so when sliced, all of the juices ran out of the meat.
Do you see a common theme here? It is so common for people to NOT allow enough time for brisket. So, cook your brisket shooting for it being done 6 hours before your event, and you should not have to compromise.
The reason she is asking for time, is because everyone needs to know what time they should start the darn thing! I don't think she was planning on cooking by time-only. Internal temperature is always what you go by for pulling from the smoker. I would go by 1.5 hours per pound at 225, and plan on it being done by noon on Saturday, then a rest in the cooler until you are ready to slice before 5:00. If it's done later, you'll still have plenty of wiggle room for your 2 hour minimum rest. If it's done early, take it out and double wrap in foil. Turn the smoker off, and leave the door open for 30 minutes to let it cool down. Turn the smoker to 140, put your brisket back in (in a foil pan would not hurt, to help insulate against heat from the bottom), and keep warm until about 2-4 hours before your event, at which time you can transfer to a cooler to rest.
I know you've got a 3D, so in theory you could program in changing the smoker temp to 140 when the internal temp reaches 195, but that will overcook your brisket. Even though the digital controller will shut the element off, because these smokers are so well insulated, the internal box temperature will probably remain up toward 225 for a couple hours. And your brisket will go way past 195. Maybe others here have a suggestion on how to program this, for cutting it off at a lower internal temperature, switching to 140 and hoping the final internal temp will end up at 195, but I think the old fashioned way works best for brisket (when you reach your desired internal temp, remove the brisket).
