When in the timeline Alien: Earth set?

This places it in the early 22nd century, a few decades before the crew of the Nostromo encounters the Xenomorph.

To put it in context with other films in the franchise:

• It takes place long after the events of Prometheus (2093) and Alien: Covenant (2104), which explore the origins of the Xenomorph and the Engineers.
• It is also set before the events of Alien: Romulus (2150s, between Alien and Aliens), which bridges the gap between the first two Alien films.
• The Alien vs. Predator films occur even earlier in the timeline, in the early 21st century (2004 and 2010). Not that we count these films...

Therefore, Alien: Earth (set around 2192) will showcase a world where humanity is largely unaware of the Xenomorph threat, and the Weyland-Yutani Corporation is still in its formative stages. 

The show will likely explore the early days of the company's colonization efforts and the potential dangers that lurk in the unexplored reaches of the galaxy. 

We might see the introduction of characters who will later play significant roles in the larger Alien universe, or witness events that foreshadow the coming conflict between humanity and the Xenomorphs.

The setting of Alien: Earth also presents an opportunity to delve deeper into the mythology of the franchise. We could learn more about the history of the Engineers, the origins of the Xenomorph, and the ancient secrets that have been lost to time. 

The show could explore the philosophical implications of encountering a species that is so fundamentally different from our own, and examine the potential consequences of our own hubris and thirst for exploration.