It depends on how big & what temp you're using. I can do a small, 3-4 pounder in 5-6 hours at 250-275 degrees. I think the last time out I had a bigger one, though. It's done when it's to temp, not by your plans sometimes, unfortunately. And burnt ends are actually cubed, tasty nuggets off of the point-end of a brisket. You can almost duplicate them with a chuckie, but they're not quite as good as the real thing. The upside though, is that you don't have to cook a WHOLE brisket (or even a point) to get them. You can just make some nice, pulled beef BBQ if you cook it like a pork butt though, like I was sayin' before.
My "faux" burnt ends (chuck roast)