If you were cooking it whole, yeah, I'd say 250F for 8 to 12 hours, preferably over smoke, or simmered at a low heat for nearly that long.
Since you've cut it up it wouldn't take that long, but still, it's the kind of meat which you should keep cooking for as much as another hour after it reaches the internal temperature which you would normally consider 'done', until it's fork-tender.
Brisket contains a lot of collagen. If it's cooked the way you'd cook most beef, the collagen will seize up and make it very chewy at best or tough and dry at worst. But if you can hold it at or around the 'done' heat, the collagen slowly breaks down into a soft, uncious gelatin.
Once you've got your beef to the fork-tender stage, my recommendation, for at least some of it, is to mix it with BBQ sauce and serve it on buns with corn and cole slaw.
They say of the Acropolis where the Parthenon is...