In the beginning a long long time ago, I did both. I would start with a little before and massaging it in to get good circulation…then punch, then massage for removing damage afterward.
Then, as I improved, I came to the point of just massaging my hands and only using the stuff when I did too much or injured myself.
I had classmates who darn near bathed in the stuff…I personally think they would use it because massaging it into your hands felt a lot better than punching gravel…their laziness. The ones who progressed tended to do the same thing I did and eventually only needed to use it a lot when changing levels (going from gravel to rock - small rock to bigger rocks in the bag…)
Jow is normally applied before the start of training and allowed to air dry. Then you do whatever, bag work, iron palm etc. Once you have completed the training cycle you apply the Jow and again allow it to air dry.
Jow is a generic name for a variety or perhaps I should say family of herbal recipes used to aid in the conditioning of ones hands arms etc. It is a type of bruise medicine which will aide one in healing more quickly after training. Some variants will also assist in the toughening process causing whatever body part to become stronger. Some are also said to aide in making the bones denser. Most traditional Sifu have their own recipes which are tailored to their art.