Hi Scott,
You can keep meat hot for at least 4-5 hours, and warm for much longer, by wrapping it in plastic wrap, then aluminum foil, then placing it in a small cooler wrapped loosely with a towel.
Last weekend I took two pork butts off the WSM at 9am, wrapped them like this, and they were still warm at 4pm when I opened them up. If you take the brisket off in the early afternoon and eat around 6 or 7pm, it will still be hot when you open it.
I think the taste and texture of meat always improves when it is left to rest after cooking...