That should be plenty time to get done, should be good and tender. Hint, wrap in tinfoil and put back on grill for the last 2 hours or so, it will rejuvinate any dried out portion.
Ohhhh, yeahhhh! The brisket turned out great. Internal temperature hit 190 degrees exactly 30 minutes before meal time. We took it off of the heat and let the juices circulate before slicing. Wrapping it up in tin-foil 2 hours before take-off seemed to work great. (Thanks for the advice eastforker.)
1/4 inch perfect smoke ring all around.
I need to do this more often.