I started putting my Aussie's outside at 4 weeks old. The weather was in the low 60s (warming up to high 60/low 70) and they seemed quite comfortable. They sounded like they were cold when it started to get dark and the temp dropped to the low 50s, but they are now 6 weeks and don't seem to notice when the temp drops.
However, we have been a bit slow to get the coop ready for the girls (bought a house, planning a wedding and starting a flock - all at once!), so they have been sleeping indoors, since the cage they are in isn't very good for nighttime. I'm afraid I'm raising some princesses. Last night the temp was in the 70s, so plenty warm for them and they all started their plaintive peeping as soon as dusk arrived. They quieted down right away once they were placed in their cardboard box, and they even lined up to be carried inside!
Aren't they going to be surprised now that the coop is ready?