PNF stretching

I know that before training or a game that you do not recommend static stretching as it is believed that static stretching temporarily weakens muscles.I have read that you do use PNF stretching before a workout or game.Why is it ok to use PNF stretching?Isn’t there a static stretch component after the isometric contraction?Is it ok to static stretch at that point beacuse of the window of muscle relaxation ?How long do you hold the static stretch after the isometric hold so you do not stretch longer than the window of relaxation induced by the isometric hold