Brisket and pork butt

I've never smoked brisket and pork butt at the same time, but I have tons of experience with both.  Pound for pound, my briskets cook faster than my pork butts.  Could just be me.  In the past month or so I had a 14 lb brisket take 17 hours, a 9.2 lb butt take 19.5 hours, and a 10 lb butt take 21.5 hours.  All were smoked at roughly 250F. 

You could stagger their start.  I'd target them to finish a couple hours before your drive, just for a built-in cushion.  They'd be fine for a 3+ hour rest if they finished on time or earlier. 

I always cook my pork butts well in advance. Pull, vacuum seal in 3lb portions and freeze. I always have about 40lbs of pulled pork in the freezer. They freeze very well and reheat easily.

I have done briskets the day before and rest them whole overnight. Rewarm them whole the next day in the smoker or a oven set at 200 to 225 then slice.

To me trying to cook these two meats on site the day of the event is asking for trouble due to the length of time these take. Very unpredictable length of time at that. Also both require a good amount of resting time.

Of course the other option is staying up all night the day of the event and go 24 hours without sleep.