I'm probably one of the least experienced here, having done 3 full packer briskets (flat and point). But I've done a lot of reading. The first two smokes produced somewhat dry, leathery briskets. I was pulling them precisely at 195.
Couple weeks ago, I cooked my third brisket near high heat, a majority of the smoke. I couldn't get my WSM to settle down. The WSM temp kept wanted to flirt with 300-325.
To make a long story short, I foiled the brisket around 160 and left for several hours. When I returned, the brisket was reaching 215 in spots, and above 210 everywhere. While the probe slid in "soft butter" smooth, I was certain I had overcooked the brisket. I anticipated a very dry and leathery brisket once again. To make matters worse, it was 2 hours before the chow time, so I wrapped in a towel and put it in a cooler, figuring this would further cook the brisket into oblivion.
Perhaps you can sense that this story has a unpredictable end? It did. The brisket was not only the best I had done, but I fear it may be the best I ever do! It was fantastic! I simply couldn't believe that it came out so well! Juicy, tender, flavorful. Simply wonderful.
So after reading it over and over again, I've come to the realization that temperature IS only a guide. To tell when your brisket is done, I would start looking at the temp about 180 and probe it every 30 minutes. It must have the "soft butter" feel when probed. That makes it difficult to prepare for any particular "eating time", but remember to let it rest. That should carry you into the dinner hour. It's also amazing how long they can rest and still be steaming when they come out of the cooler.
Your mileage may vary, that just my experience.