How long does it take for second degre burn scars to fade?

Depends: 2nd degree burn is a wide range of injury from fairly mild to very severe. A small mild second degree burn will leave a scar that fades quickly while a severe full thickness burn with less than ideal treatment may leave a very bad scar or may have needed skin grafting and may never fade completely and may require silicone compression or plastic surgery to completely eliminate.

Depends on depth: There are different depths of 2nd degree burns. Both will require weeks to months in most cases. Use of silicone gel products to keep site moist often reduces redness faster.