When to move chicks to an outside coop

[jaswiggins]

I asked this in the Chick section, but thought I'd try here too.
I have five 9.5 week old chicks outside in our new 8x8 coop (still under slight construction), and seven 4.5 week girls inside in a crowded, getting stinky brooder. Turned off extra heat source (red heat lamp) yesterday for the little ones and will turn off heat in the hallway (where they are located) tomorrow. I live in CT and temps are around 75 during the day and 50 at the lowest at night. When I move the little ones out I plan on moving them into a dog crate in the coop for a week before directly introducing them to the older girls.
My question is, when can they go out? They are not quite fully feathered, but getting there. I could run a heat lamp at night via extension cord (electricity not yet installed) but not really a fan if that bc of fire hazard.

 

[lightchick]

They can live outside now. I moved my chicks outside today and they are only 3.5 weeks old.
They are also without a heat lamp and the temp here goes down to 50 degrees at night.