As long as the incision site looks healed and clean its fine. A technician can easily remove the
sutures. Worse case the
sutures are embedded (meaning the skin grew over them). Being only 20 days, they probably can still be dug out, its just a little more difficult, It is even possible the stitches aren't even there anymore as most kitties will remove them themselves given the chance...sassy kitties. However, even if thats the case, still have a technician check it to make sure.