You may counter a Boxer as soon as he makes a move

For systematic training, let us stylize a Boxer's attacks as jab-jab-cross. First we learn to counter at Point 3, i.e. we deflect his two left jabs, and apply "cover and strike" as he executes his right cross. Next we counter at Point 2, which is deflecting his first jab, and cover and strike at his second jab. Then we counter at Point 1, covering and striking him as soon as he makes the first jab. Irrespective of at which point we wish to counter, we must cover an opponent adequately before se attempt to strike him.