India 42,
I think the word "approximately" was used by the FAA attorney in an "abundance of caution" (as we lawyers like to say) to avoid being locked in to the exact times stated. It seems to me that if the chronology set out was reasonably accurate, the use of the word wasn't necessary and the lawyer was simply being overly cautious.
By the way, I think people are making too much of "a frolic of one's own." As enoon alluded to in post 355, under US law the FAA's use of that phrase wouldn't absolve NW or anyone else of liability had the flight come to an unfortunate end. My sense in reading the revocation letters is that the FAA attorney didn't intend to use the phrase as a legal term of art, but simply to convey in vivid language that the pilots were off doing something that they shouldn't have been doing, regardless of whether it related to airline business or not.