I agree with running a bit lower chamber temps...smaller cuts can climb through the 150-160* range pretty fast, and brisket is a very tough cut of beef, which needs to come up to temp slow in order to get that tender texture you'll be looking for.
I haven't smoked one that small, but I have done alot of lean-trimmed/separated point & flat smokes from a full packer.
Now, I'm talking about a 13-16+lb packer to start with, and about 30-35% of this being fat and the connective tissue around the edges. Figure about ~5-5.75lbs for each cut, and they were running into the 10-12 hour time frame at 210~230* grate/chamber temps, for foiling at ~180*. Then, to steam it to a finish temp of ~195-200*, would take another 5-6 hours.
At temps below 225-235*, I would plan for at least 2 hours per pound...that's just been my personal experience.
I also have done a few brisket smokes where I only smoked to ~160*, foiled and held @ 200* for 10-12 hours for pulled beef from the flat...this is now my preferred method, as it takes much less tending and temp checks.
The flat is very lean compared to the point, so it takes a quite a bit of time to break it down enough for pulling. The flat can be easily pulled once it has been foiled @ 160* and is held at 200* for 8-10 hours, and has then rested in foil & towel wrap for an hour or so.
Keep the chamber temps as even as possible...smokers will have temp swings, but don't sweat 'em. Keep the door/lid closed as much as possible, as you want to keep the heat in the smoke chamber. Opening the smoke chamber adds alot of cooking time with each occurrence.
Let us know how it's going for you.
Happy smokes, brother!