Your not-fully-feathered chicks will benefit from early exposure to cooler temps by having their feather growth stimulated. This is to say, gradual acclimatizing will cause feathers to grow in more quickly.
The secret to doing this without over-chilling your small ones is to avoid cold drafts and wind. A partially feathered chick will do fine away from a heat source for spells, but a chilling breeze can suck their body heat away very quickly, and you do not want that to happen.
I've watched day-old chicks frolic away from their heating pad cave or broody hen on a chilly 50 degree day without any apparent discomfort. I raise my chicks outside right in my run with just a heating pad for them to warm up under, and just recently watched a single chick being raised by a broody hen. Broody raised chicks do not spend four weeks, day and night, hiding under their mama.
Chicks are tougher than we sometimes give them credit for.