How long do blessings last?

I recently attended a Tibetan Drinking Kagyu Buddhist retreat. During that time the visiting Rinpoche blessed several items, and I was told by His Eminence that one can renew the blessing of statues by placing them in a small bowl containing a little bit of saffron water, and then dribbling some of the water over the top of the statue. I neglected to ask how often this should be done. Does anyone know?