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, although there's no specific dates, very early 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. The story makes all the following events feel like they pass in a matter of months but the real-world events were spread out over the better part of a decade and, with no dates pinned down, there's no reason not to use them to clock the progress of the fictionalized events.

1972 AD - 1979 AD
We know this because, although there's no specific dates, very early 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. The story makes all the following events feel like they pass in a matter of months but the real-world events were spread out over the better part of a decade and, with no dates pinned down, there's no reason not to use them to clock the progress of the fictionalized events.
Later, Ron goes undercover at an event where the real-world African-American civil rights leader Stokely Carmichael a.k.a. Kwame Ture gives a talk sponsored by the Black Student Union of Colorado College. The black activist did speak in Colorado Springs in 1977 AD and the real-world Ron Stallworth did attend; though it was not at Colorado College.
(HOWEVER, the Black Student Union of the college did invite him in April of 1979 AD, though this doesn't really work within the film's timeline.)
Eventually, Ron first makes contact with the hate group the Klu Klux Klan. In the real-world according to Stallworth's own words in a 2006 interview, "This started in October of ’78, this conversation." So this point of the narrative must be in October of 1978 AD.
The movie's climax is the conclusion of this investigation, which lasted "eight or nine months or so" in the real world. Therefore it ends around June or July of 1979 AD.
10.1978 + 8 months = 6.1979
or
10.1978 + 9 months = 7.1979.
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.
This Slate article examines its exact setting.