I’m not in New England but I’ve had chicks go through overnight lows in the mid 20’s at less than 6 weeks. I brood in the coop and have turned daytime heat off after 2 days and overnight heat off at 5 days in the heat of summer. There are a whole lot of different things I consider before I decide when they can go without heat, but that stuff seems to frustrate you so I’ll make it simple. If your overnight lows are above freezing they can go without heat at 6 weeks. If your overnight lows are below freezing, put them out at 7 weeks. Both of these are extremely safe. I never wait that long.
x2 I never wait that long either. My first batch of chicks were 5.5 weeks old when I evicted them. At that point it was them or me! Their coop wasn't even finished, and it was April 1st. We live in Northern Wyoming, not too far from Yellowstone Park, in Basin between the Pryor, the Big Horn, and the Absaroka/Beartooth mountain ranges, so April here can't be called balmy. We often have winds in excess of 60 mph and that's year round.
I put a lamp out there for them the first night, and had a wireless thermometer transmitter with the receiver in my room on the nightstand. I watched all night long as those temps dropped and dropped. I kept jumping out of bed, throwing my coat on over my jammies, pulling on my boots, and going out to check on them. They were fine - snuggled in a pile of beaks and feathers near the pop door - and nowhere NEAR the heat lamp. I expected to find chicken-cicles when I went out in the morning, but they were perfectly fine. They'd eaten, had some water, and were waiting for the pop door to open so they could go outside. The next night it was the same story, except I only got up once to check on them. It was 14 degrees that night. So that morning I took out the heat lamp. If they weren't going to use it, I wasn't going to risk it. That night it snowed. We got our last snowfall on June 6th. If I'd kept them inside until it was "safe" to put them out, they'd have practically been laying eggs in the brooder. Many of those girls are still out there 3 years later, providing eggs and entertainment. I gave 8 of them away to a lady who lost her entire flock to a pack of marauding dogs. The roos went into the freezer. But the ones I kept, and the ones I gave away, are still just fine.
We have to remember sometimes that we are raising chickens, not little Divas. It's so hard not to base their comfort on our comfort levels. And the long we wait to make the transition to the outside facilities, the harder it is on them. They don't like change, and going from a lit, warm, noisy environment to what they'll have to live in is quite a shock. That is so stressful for them. Most times they huddle together not because they are cold, but because there's security in numbers.
All of my subsequent chicks have been raised outside in an enclosure in the run, exposed to all the activities of the adults, the air, the surroundings they'll be in, the flora and fauna in the litter, and with a total understanding of day/night cycles. When the sun goes down, they go to bed, and they sleep all night long. No eating, no running around, no picking at flockmates - they just go to bed. When the sun comes up, they get up, rested and ready to start the day. I'll never go back to indoor brooding. I have three chicks out there right now (in with 8 others we bought when they were a couple of days old) and those three chicks went out to live as soon as they were hatched, dried, fluffy, and knew how to eat, drink and get warm.
Heat stresses chicks and chickens much more than chilling. In fact, a little chilling is actually very beneficial for them. @Ridgerunner has often remarked that the chicks out in the brooder set up he has do very well, even if there's ice in the water on the other side of their brooder. They have cool zones, and warm zones, and like in my set up they very quickly learn to regulate their own comfort.
Yours should be just fine. The hardest part is letting go, getting them out there, and sitting back with a glass of wine while they sort it all out for themselves. The longer you wait, the harder that is on both you and the chicks! So relax - if they are protected from predators they should be good to go!
