If it were ME doing your 14 lb packer (and it isn't mind you) I'd put it on the pit at 225d-235d late at night. I'd let it cook through the night. When I got up in the morning, if it looked nice and dark, I'd wrap it in either butcher paper or foil, then ramp up the pit temp to 275 and start checking it after a couple of hours for probe tenderness.
I'm certainly no brisket expert, but that's what I'd do.
Even if it comes off the pit at 2 and only rests for an hour, just let it rest in the counter. Holding it in the cooler just prevents it from cooling off too fast, but an hour on the counter will still let it be nice and hot for you when you slice it.
Bottom line.....don't stress it. If it doesn't get nice and tender until 5 and you don't get to tear into it until 6......is anyone gonna be any less happy really?
Just tell em, "It's BBQ. It's done when it's done. Have another beer."