When Does the Film "Blade Runner" (1982) Take Place?

"Blade Runner" is a science fiction film written by Hampton Fancher with David Peoples [adapting "Do Androids Dream of Electric Sheep?" by Philip K. Dick] and released June 25th, 1982. 

It takes place in the year: 

2019 AD 

We know this because the replicant (i.e. synthetic person) Leon Kowalsi asks, "My birthday is April 10, 2017, how long do I live?" to which Rick Deckard replies, "4 years". So we know it is currently before April of 2021 AD. 

The other main replicant characters in the film were built in early 2016. It is said multiple times in the film that replicants have a "4-year lifespan". The plot is mostly concerned with their impending deaths and must therefore be earlier than early 2020 AD. 

Furthermore, after the opening credits, the audience sees an extended title card that begins, "Early in the 21st Century..." which goes on to explain some of the setting. Immediately after this, there is a white-on-black title card reading "LOS ANGELES NOVEMBER, 2019". 

[Some fans place it on the fictional Alien vs. Predator timeline either between "Predators" (2010) and "Prometheus" (2012) or between "Predators" (2010) and "Blade Runner 2049" (2017) or between "Predators" (2010) and "Soldier" (1998).] 

Because of creative differences between the film's director Ridley Scott and the film's studio Warner Brothers, there are many slightly different versions of this film under both nicknames and official names. The differences are mostly stylistic and change the film's tone. 

Among these changes is the absence in some of the opening extended title card that places it "Early in the 21st Century". It is replaced with a quote from a "NEW AMERICAN DICTIONARY" 2016 AD edition, something that could not have existed yet in 1982. 

All keep the "LOS ANGELES NOVEMBER, 2019" title card, so the film's time setting is not significantly changed in any of these versions.