What we have here are (three) two-second clips from a Lockheed-Martin video of a ground attack rocket test. These clips show the missile just before it impacts the target, in this case a tank. Blutarsky noticed a small white flash just ahead of the missile near it's projected point of impact. nougabol tells us that it is the "Pressure wave from the missile hitting the tank." Since the pressure wave hits the target before the missile, you have advance notice that the missile is coming. Since the missile is supersonic, that time is very short.