sperm mobility and marijuana

My husband and I are currently TTC for the past 6 months. We have 2 beautiful children together and have had 2 miscarriages. We have been together 11 years never using protection. My husband smokes marijuana every day from the time I met him 2-3 times on average a day. I have done many tests and seen many doctors there is nothing wrong with me. I'm aware marijuana use is not good for men's sperm. My main question is how long will he have to quit before his sperm will be up to par?