

Pre-space age yinrih history is somewhat messy right now, but current lore has them achieving spaceflight 5 millennia after achieving sapience. Given their much longer lifespans (~723 Earth years) this would be like humans going from crudely knapped flint hand axes to orbital flight in 500 years. So they’re in space before humans leave Africa. My (admittedly weak) justification for this is that they start the game with writing unlocked, there’s no ice age to impede the invention of agriculture, and religious zeal is one powerful motivator.
I don’t have any specific dates for hot air balloons, although it is the first thing they mess around with. I do have them playing with Jules-Verne-esque manned projectiles around the year 1406 AK (about 2000 Earth years after the first evidence of written language). This begins a period marked by high casualty rates among research monks and their lay assistants. These brave souls are known as the Cannonized [sic] Martyrs.
There are only two sapient species in the Lonely Galaxy, humans and yinrih. There is a closely related non sapient species to the yinrih, closer even than chimps are to humans, and the question of why the yinrih are sapient and the tree dwellers are not drives a lot of philosophizing on the yinrih’s part. The Atavists in particular resent the burdens of existential dread and moral guilt that come with having a rational soul and wish to return to being irrational animals.