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:
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 2 episode 6 "The Sound of Thunder", which takes place in 2257? AD.

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 2 episode 6 "The Sound of Thunder", which takes place in 2257? AD.
2257? - 18? = 2239?.
It is the second-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).