When Does "Star Trek: Short Treks: The Brightest Star" (2018) Take Place?

"Short Treks: The Brightest Star" is a science fiction short film written by Bo Yeon Kim with Erika Lippoldt that released December 6th, 2018. So when is "The Brightest Star" set? 

It takes place on the fictional Star Trek timeline in the year: 

2239 AD 

We know this because it depicts First Officer Saru's initial interaction with Starfleet and he tells Michael Burnham, "For 18 years, I dreamed of returning to my village." in "Star Trek: Discovery" season two episode six "The Sound of Thunder" (2019), which takes place in 2257 AD. 

2257 - 18 = 2239. 

Although the famous "stardate XXXX.X" captain's records that open most episodes and some films were mistaken for years on the Gregorian calendar, there is no one-to-one relationship between them. As identified in the biography "Gene Roddenberry: The Myth and the Man Behind Star Trek": "They marked off sections on a pictorial depiction of the known universe and extrapolated how much earth time would elapse when traveling between given points, taking into account that the Enterprise's warp engines would be violating Einstein's theory that nothing could exceed the speed of light. They concluded that the 'time continuum' would therefore vary from place to place, and that earth time may actually be lost in travel. 'So the stardate on Earth would be one thing, but the stardate on Alpha Centauri would be different,' Peeples says." so they are relative to long distance travel and not an absolute calendar. HOWEVER, actual years on the Gregorian calendar began to be used later. 

It is the earliest chronological short film in the Star Trek universe and can be watched at its timeline point or as an extended flashback after "Star Trek: Discovery" (2017).