When do I start massaging my incision site to reduce scars? (Inframmamary surgical site; I'm over a week post op)

You will definitely want to ask your plastic surgeon first to find out what he/she recommends for optimal healing of your incisions .While gentle massaging of scars can be helpful, I find that most of my patients do not need to do this. The most important thing you can do is to keep tension off the incision so it doesn't pull and widen. I have my patients apply surgical tape over their incisions to avoid tension and to keep them from focusing on the scars during the healing process. Once the incisions are fully closed, I will often times recommend a high-grade medical scar therapy ointment to take away redness and keep the scar from raising. I stock Scarless® at my practice scar treatment. Embrace is another scar therapy that you can look into. 

Its best to ask your plastic surgeon about his/her specific recommendations.  I generally recommend a scar massage regimen 4 weeks after surgery.  Best wishes for a speedy recovery.