Maybe i misinterpreted the comment. But from my point of view he was saying that it couldn’t be done. We aren’t making something huge.
I think many of us underestimate how long it takes to put something together, even a small coop or doing some minor work on the run. It always takes me 3-4x longer to assemble something than advertised. So anyone who can get it done fast is impressive.
Oh yes, as to your original question, 8 weeks should be fine to go out into the coop, but as some of the earlier posters noted you need to acclimate them to the temperature difference.