It's no secret that Zack Snyder's movie Rebel Moon, currently out on Netflix, was originally going to be a Star Wars movie. Shortly after Lucasfilm was sold to Disney, it was announced that multiple spin-offs would be created in addition to the sequel trilogy. Several filmmakers got a chance to pitch their ideas for a Star Wars movie. Among those who got a chance to pitch a spinoff idea was director Zack Snyder, who described his pitch as a more mature take on Star Wars and as Seven Samurai set in the Star Wars universe.
Ultimately, Lucasfilm passed on the idea, so Snyder eventually repackaged the concept as an original movie set in an original universe. That movie (or at least the first part of it) has been released on Netflix. While it is an original movie, it's easy to see the influence of Star Wars on the story. Using some context clues from Rebel Moon, we can even make a good guess as to when in the Star Wars timeline Snyder's Star Wars movie would have taken place.
Before we get started, it should be noted that this will involve spoilers for Rebel Moon. Also, the movie was split into two parts with the second part scheduled to come out in April. It's possible that once we get to the second half of the story, there might be more context that makes it apparent that some of this will be incorrect. But for now, here's the best guess for when Rebel Moon would have occurred in the Star Wars timeline.
First, to get the most obvious thing out of the way, the title suggests that the Rebels would have played an essential part in the storyline. We also get an opening narration that would have probably been the title crawl if this had been a Star Wars movie that describes a galaxy-wide governing body known as the Motherworld.
It's pretty easy to see the Motherworld as a stand-in for the Galactic Empire. There are references to a group of insurgents rebelling against the Motherworld. We meet the leaders of the rebels later in the movie. Given these two points, it's pretty safe to assume that the film would have taken place in the original trilogy era when the Empire was trying to stamp out the Rebel Alliance.
Another key figure in the movie is a sword master named Nemesis, whom we meet partway through the film. The introduction leads into an action scene that results in Nemesis taking out weapons that legally aren't lightsabers but are clearly meant to be lightsabers. Given this character, it's easy to see a Star Wars version of the movie where this would have been a Jedi who had gone into hiding after Order 66 but is willing to help fight for the cause.
So, if there's a Jedi character in hiding, then it would be likely that the movie would have taken place between Episodes III and IV. However, the events of Snyder's version would have taken place closer to the prequel trilogy than the start of Episode IV.
Two of the main characters in the movie turn out to be former members of the Imperium army that fought under the Motherworld. It's easy to see these two characters as ones who would have fought in the Clone Wars for the Galactic Republic but turned away after the Republic was reformed to become the Empire.
Ultimately, it might be better for the movie that it wasn't a part of Star Wars. As the story expands with Part II coming out later this year and the inevitable sequels that will be coming after that, the story will probably drift further and further from the Star Wars elements that inspired so much of it.
So much of the new Star Wars that we get today is limited in some ways because it takes place in between other stories, meaning that it has a set endpoint that it is heading toward. But with Rebel Moon being its own thing now, the story can go in any direction and is not beholden to the fact that it will eventually have to tie into the status quo of A New Hope at the end.