How early do you remove the nest box. Kits are about 3 1/2 weeks now. We're in Central TX, so while it's cold, it's not near as cold as most of you. No lower than mid 20's at night so far.
When I see the kits are starting to come out of the box, and it's cold (like now :x ), I tip the box over on its side for a few days, so they have somewhere to huddle. Once all the nesting material has fallen through the wire, I take the box out.
Summertime, I just take the box out at about three weeks.