It is set after the Civil War, and it's VERY clear it is if someone is even mildly paying attention to the film. However, given the state of education in this country, especially American History (and more specifically pre-1900's history), I can see where some confusion might arise, but to audiences in 1946 (only some 80 years removed from the war and post-Civil War South reconstruction) there would be no such confusion. But I highly doubt the film is part of the Netflix deal. I know the film was given a 4K restoration a few years ago, but I'm not exactly sure why the company bothered given the state of the current leadership within the company, and comments they have made in the past. It's pretty clear SotS will never see the light of day under the company's current stewardship.
If you really want some good insight into the movie and the modern controversy over the film I highly recommend Jim Korkis's excellent book, "Who's Afraid of the Song of the South and Other Forbidden Disney Stories."
Yancy