It is not possible to say in general how long it takes. It depends on how deep and how much trauma there was. It can take from one week to one year and in case of big wounds such as after serious accidents, burns etc it can take even more. The primary goal of our body is to survive and that is why the body makes sure our injuries are immediately fixed to prevent an infection and restore normal skin function.
Wounds are sealed with scar tissue as quickly as possible. In case of mild injuries, the skin heals back to normal. More serious injuries are filled with scar tissue that doesn’t go back to normal since our body doesn’t feel any need to replace scar tissue with normal skin. Scar tissue is merely an esthetic problem. Repeated microneedling makes the body remodel the scar by making microscopic injuries in the scar that trigger new healing processes – as a result, the scar often softens and regain a more natural color. Microneedling tricks the body to re-heal the scar. Deep scar will however never disappear, it will only improve in appearance.
Here is a graph that shows the stages of healing. Keep in mind that it pertains to serious injuries and wounds. Scroll down to answer 11:
https://http://forums.owndoc.com/dermarolling-microneedling/when-can-i-resume-using-my-regular-face-cream-after-rollingm/a>