When Does "BlacKkKlansman" (2018) Take Place?
"BlacKkKlansman" is a historical fiction film written by Charlie Wachtel with David Rabinowitz, Kevin Willmott, and Spike Lee that released August 10th, 2018. So when is "BlacKkKlansman" set?
It takes place in the years:
We know this because very early on in the movie the real-world Detective Ron Stallworth is hired at the Colorado Springs Police Department. This happened in the real-world in November of 1972 AD.

1972 AD - 1979 AD
We know this because very early on in the movie the real-world Detective Ron Stallworth is hired at the Colorado Springs Police Department. This happened in the real-world in November of 1972 AD.
Later, Ron first makes contact with the hate group the Klu Klux Klan. In the real-world Stallworth's own words in a 2006 interview, "This started in October of ’78, this conversation." So this point of the story must be in October of 1978 AD.
The story's climax is the conclusion of this investigation, which lasted "eight or nine months or so" in the real world. Therefore it ends in June of 1979 AD.
10.1978 + 8 months = 76.1979.
The film ends with an epilogue made mostly of footage of the then-recent Unite the Right rally and subsequent violence. Several labels appear over this footage in title cards with August of 2017 AD dates.