I can't remember the last time I used a flat for chili, but I absolutely LOVE brisket point chili. I have used it prepped just about every way imaginable before putting it in the chili; smoked completely then cubed, smoked for merely two hours then cubed, cubed raw and browned in the pot. My two favorites are smoked for just a few hours (usually 2) then cubed, or cubed raw and browned in the pot (no smoke though).
Personally, I've found the raw/browned and incompletely smoked brisket points become more melt in your mouth tender when braised in the chili. The chili is done when the cubes still have structure, but just dissolve when you bite into them. That can happen anywhere from 4 - 6 hours. I usually count on 4 to 5.
The reason I don't like using a fully smoked brisket point is that it breaks down too much when simmered for a long time. When a brisket point is fully cooked, the chili is ready in 2-3 hours. Something magical happens to chili though when it has been simmered for at least 4 hours (same thing happens to tomato-based spaghetti sauce). The flavors become more blended and the ingredients take on a oneness that cannot be hurried by higher heat or shorter time.
If you want a chili that will knock your socks off, use an incompletely smoked or raw brisket point and simmer it for at least 4 hours.
Dang, I'm suddenly hungry for chili! Just made a huge pot of turkey vegetable soup yesterday, so it will be a few days before I can scratch that itch.