If you crouch and wait for the guard to come and shoot just when he finds you, and you grab the keycard while crouching and do the normal stuff after - it is easier and may have a chance to be faster. Right now, I got it down till around ~19.3 - 19.5 seconds on average for the Section (Spawn until opening the door with the keycard), and I have only been practicing for ~20 minutes. Right Now, the world record is like ~18.76 on that section. I think with a bit of practice, it can be done. (What I mean is instead of shooting the camera and guard, why not only shoot the guard?) This is a video to show an example of the Strat: