That culture has time travel, and they’re wasting it on a scenario where they’re possibly starting a temporal paradox that will wipe out their entire timeline?
Dudes. A working time machine is also effectively a faster-than-light drive. Send probes out until you find a planet…
No, it doesn’t effing matter how long that would take. You have a time machine.
…that’s not developed past the Cambrian era. Terraform that.
Again. Time constraints do not matter. You have a time machine.
Then, once it’s open for business, move everyone to that, secure in the knowledge that there isn’t anything in the ecology there that you didn’t put there in the first place.
In fact, do this ten times. Give people some room.
Remember: you have a time machine.
PS: I’m skipping over the environmental doom-and-gloom because, well, modern media. Besides, the title’s bad enough, all on its own.
Think about it for a second.