wells,,,lol,, sorry
chickens can stay in the house forever,, if you can stand it lol,, and out as babies in maine i would wait until their FULLY feathered, and a good no-draft coop is ready. did ya get the snow last night? hehe , is 70 something here right now lol
and before letting them out in the cold, i would make sure you dont keep a light on them for 2 weeks before moving them,, in fact, while in the house, i would only keep a light (heat light) on them for a month at the LONGEST. or they will never acclimate to the outside. if your house stays way warm,, after their wing feathers come in, i would only turn the light on at night when most in maine keep the house cooler.
BUT ,, wait for the pro's to answer too,, i do things a little different,, with about the same results ( if not better hehe )