Like diabetes, it takes different times for different people, depending on age, immune system, how bad someone has let them get, how well they are protecting their feet/hands day by day (thick woolly socks on one end, ditto gloves on the other). For me, a temporary stop in taking hot baths, and twice-daily application of ointment, does the trick in about 4 days, but we are all different. As for can you use it on broken skin - I don't know. I never let mine get to that stage. If I did I would, but that's not to say it's a good or bad idea.