I would say you might be looking at an eight hour cook or less. Like everyone says on this board, all Briskets are not alike.
I do mine all fat side up and pull it when it hits 185º. I wrap mine in foil, wrap it in towels, and place it in a dry cooler. Mine stay in the cooler for a few hours until its dinner time.
Use the Minion method as well, it's great, fast and simple.
When all is said and done you probably wont have any left overs for the next day.