Brisket time

My last 14.5 pounder only took 7 hours at a grid temp of 240... hopefully, you don't have the unusual brisket that cooks really fast.

As you know, others will tell you that it can take up to 2 hours per pound so you could be looking at 30 hours - although that can be shortened by rasing the temp when you get home.

So, given your schedule, I would do just what you suggest.  Get the egg stabilized as low as possible (220 or so) and put the meat on as late as possible before leaving for work.  I would also put it on cold - essentially straight from the refrigerator. It should take a long time for the meat to get much above 190 when the cooking temp is only 220. 

Then - as you already suggested - adjust as needed when you get home in the morning.

Good luck. 

Just like @Eggcelsior, I had a perfectly cooked brisket at 0600 and a party at 1900.  I put it in the refrigerator for most of the day and warmed it in foil before I sliced it at the party.  Everybody loved it and wants me to do it again....

@TexasCrane may have the right answer for you.  I just haven't done a brisket that I purposefully cooked at 275 - 300 in an effort to avoid the overnight cook so I can't personally recommend it.  I've done it with pork butts and it works great.