The focus should be on the 1.6 sec between the first and second shot.
There was no 1.6 seconds. That is based on assuming the maximum time availible for Kennedy and Conolly to be hit by separate bullets. But on the Zapruder film Conolly is reacting to the sound of the first shot befor Kennedy is hit. ergo they were both hit by the same (second) shot. The first (miss) was about 3 seconds earlier.