At your chick's age, they're way too young to be in that type of cold. If you are able to keep them in your basement until March, that would be the easiest, simplest, and safest thing to do. If not, here's what you can do:
As they feather out, lower their temperature 5°F each week until they're at the outside temperature's temps. (10°F if you're in an extreme hurry.) You'll want them fully feathered before they go out. Because the deep litter won't be there until they're out there, everytime you clean their current space out, but their litter in the coop. Stir it up every couple of days and watch the inside temps of the litter itself.
I strongly suggest to keep them inside until March if you are able to. Another idea though, is to put a heat lamp in the coop with them if you need them out now. If putting a heat lamp in the coop, be sure it's strongly secured! Coop fires happen every year due to heat lamps, so be sure it's strongly secured! Then go from there by rising the heat lamp a little higher each week. That's so your going 5°F down each week until they're at the outside temperatures.
As they feather out, lower their temperature 5°F each week until they're at the outside temperature's temps. (10°F if you're in an extreme hurry.) You'll want them fully feathered before they go out. Because the deep litter won't be there until they're out there, everytime you clean their current space out, but their litter in the coop. Stir it up every couple of days and watch the inside temps of the litter itself.
I strongly suggest to keep them inside until March if you are able to. Another idea though, is to put a heat lamp in the coop with them if you need them out now. If putting a heat lamp in the coop, be sure it's strongly secured! Coop fires happen every year due to heat lamps, so be sure it's strongly secured! Then go from there by rising the heat lamp a little higher each week. That's so your going 5°F down each week until they're at the outside temperatures.