I use a timer for a great many things, including practice with dangerous game rifles. It is a wonderful motivator.
I will note that Bill Jordan was famous for drawing a service revolver from a specially made rig and firing a reasonably aimed shot (man size target at a few yards) in about a quarter second. So if we are talking about reacting to a beep, placing a hand in a pocket from a relaxed or surrender position, drawing, presenting as arms length, and hitting in half a second, well, I have sincere doubts. In a third of a second? I simply would not believe it.
So my assumption is that the shooter in question is either drawing from a position where his gun is already in his grasp, or is not counting reaction time.