For those transitioning chicks to the outdoors.
1. Step them down. By week 5, they should not be needing day or night temps above 75.
2. Find a cool, but not freezing cold place to "harden them off" at 6 weeks. A super cold basement, root cellar or attached garage. You want them to experience some 50 degrees temps.
3. Then, at week 7, move them on out. By then it is likely late April or early May and even up here, our temps are milder, day and night. They'll be completely feathered out and protected by a full blown, down coat. They no longer need a stitch of supplemental heating. Momma hen would absolutely not be covering them anymore had they been broody raised. Not a chance. Nature knows best.
Chickens haven't survived for 5000+ years of domestication by being sissies. They are amazingly tough critters.