OMG! I just cooked off 40 lbs. of brisket for service yesterday. It marinated overnight and I put it in the oven at 6:30 a.m. The temp was set at 300 F, for 6 hours. When the dinner cook came in at 11:30 a.m., I told him to pull it, but he didn't listen and just lowered the temp. I rescued it after 30 minutes because it would have burned. It was incredibly tender because I kept the fat cap on, but the sides were a little crisp and the liquid had evaporated.
If you don't check your product, it can go from perfect to crap in a matter of minutes. Keep an eye on your food, no matter what the cooking time. Better safe than sorry.