User blog comment:Sir Aether/PreGen Project: Redeployment Arc, Final questions, thoughts and the future/@comment-12236859-20170612143837/@comment-4558186-20170612200044

I don't think that they ever stated when Danzo began his shenanigans but im willing to bet it was not long after Hiruzen became the 3rd Hokage. Same with when Root was formed but I can see an early version of it existing during the second war.