To reinforce what everyone has said... Cook to temp. Not to time. If you need to have it done by a certain time, budget the time of smoke accordingly, and have a buffer built in. 1-1/2 - 2hrs per pound is what I typically use for brisket. If it finishes early, double wrap in foil and wrap a bath towel around it, then toss it in a cooler. I've had a 18# brisket in a cooler for 6 hours, and it was still above 140 when slicing it.
To echo Tony, do packer briskets whenever possible. Spend a couple of bucks and buy yourself some sort of FoodSaver vacuum sealer device of your choosing. Vacuum sealed and frozen brisket can be warmed back up from frozen in the FoodSaver bag in a pot of just under boiling water, and when you open the bag, it's like it just came off of the smoker. There's no such thing as too much brisket. I have a #2, and have done 20lb briskets without an issue. It can be a little tight, but fold up the edge, and it'll shrink down to fit on the rack.
Brisket was one of the first things I had great success with on the smoker, but a tiny flat is going to be an issue. I personally haven't done anything smaller than about 10lbs for a brisket. "No Peek" is great... to a point. But, you do have to check on it eventually. Each piece of meat is different. I've had some briskets that at 195 jiggle like a bowl of jello. I've had others that at 198 were still not as probe tender as I was looking for, and I've had to run them to 201-203.
I've also recently become a firm believer of the crutch. I use butcher paper, and don't wrap until it's well into the stall and has formed a nice bark. But, I was having problems with less than 12lb briskets, or pork butts losing a lot of moisture during the stall. The butcher paper seems to really fix this for me, and really gives me the texture that I'm looking for. Granted, everyone likes their BBQ different, so your mileage may vary. For me, this was the missing piece between people saying "Man, this sure is good" to people grabbing a plate of meat, and just falling silent as they cram it into their mouths with reckless abandon.
Stick with it! It's not an exact science, as each piece of meat is different, but it is something that you can handle. If I may, I'd suggest that you go get a Choice or Prime packer brisket of at least 12-14lbs. Take your time with the prep. Cut away the hard fat, but leave a nice cap. Season it, wrap it in Saran Wrap and toss it in the fridge for 3-4 hours. Then, pull it out of the fridge and toss it in your 2D at around 11PM - Midnight at 225. Go to bed. Set your alarm for 7am. See where the temp is. Should be in the 170's or so. Let it keep on trucking for a while. Around 185-190, check on it. If it's got a good firm bark, you can wrap it with some butcher paper, or just let it coast. Check on it about every hour to see how it's doing once it gets to 195. Temp will climb slower the closer you get to the set temp of the smoker.