I said it in my first post:
"This guy did it in 1min 20secs - from jump in to blow up."
But I guess you are right, it should be about engagement time, first shot to zero health.
I started the thread to get some tips, but Im already bored with updating it, and it hasnt helped by kill ratio/ability at all. In fact Im playing a lot worse now than in the video, and I havent had one kill since the day after I made it. You guys make it look easy, so will keep trying.