Timing is everything.
My teacher is pretty clear that it is martially not correct to wait, and react. It makes more sense to set them up before any contact is made so that they believe they are making the first move, and you are already in the place of advantage. It can look like waiting or like making the first move but it really isn't either.
Train hard and it'll make sense. It can't here (I hope, or I've wasted a hell of a lot of time).