How long does it take a surgical incision to heal?

4-6 weeks. At 4-6 weeks 90% or so of the strength in the incision has healed. The wound will continue to modify for the rest of your life. Thus scars fade with time.
It depends. On if you mean for complete remodeling and for the wound to look the way it is going to stay- in that case at least 1 year (some say up to 2 years). If you mean for activity, this depends. If it's a small lac on your chin for example- could get back quickly, if abdominal surgery- at least 6 weeks. Keep in mind if you smoke, have diabetes or other anti-healing diseases healing will take longer.