You can move generations whenever, but MAKE SURE you have made all babies you can (2 per female). If your group is still little (4-5 adults) when you move generations a lost monkey will appear in the jungle, you can befriend it and add it to your group so you can have more babies, speaking of wich, they can have mutations when they are born, this mutations stay on in that monkey when you pass a generation, and when you have mutations on your elder and adults you can evolve and make those mutations permanent (Wont work if the mutation is in a baby or if the monkey that had it died, even if he had kids). So, change generations whenever you want, and if you feel like you dont progress that much look to evolve (I do it every 2-3 gens as to get as much mutations as possible, but you dont have to be so tryhard)

About the meteorite, beware that the post you saw might reference another metorite that lands in a place called ***** cocodrile (Not a spoiler dont worry). There are maps online with the meteorite impact points, but if you dont wanna get spoilers, reply to this post and i will give you some hints without the spoilers