OP I too work 12 hour days. More specifically, a 16 and two 12's. I actually cram in 40 hours of work from 1500 on Wednesday to 0700 on Saturday. My ride, like yours is 6 miles each way. I have found that pacing myself one way, paid dividends in the return. If I feel the need to go fast (Ricky Bobby), I do it on the way home.