My brooder is in the coop. I’ve put chicks straight from the incubator into that brooder when the outside temperatures were below freezing. They don’t care what the temperature is outside, they care what the temperature is where they are. There is absolutely no question that they can go outside now or could have seven weeks ago as long as you don’t have adults out there that would be an integration issue. The only question is do you still need the heat lamp.
It’s hard to tell people when they should be able to put their chicks out without heat. I don’t know what your coop looks like. Do they have good draft protection and good ventilation, which means openings up high? If you do, you have a great start.
The other issue is acclimation. I keep one end of my brooder toasty but let the far end cool off as much as it wants. There have been times I’ve seen frost down there. The very young chicks stick to the heated area but after a couple of weeks they’ll play in the cold end, just going back to the heat to warm up when they need to. The result is that they are used to colder weather. They can handle it. I’ve had five week olds go through nights in the upper 30’s for a low and days with a high in the mid 40’s. I’ve had chicks less than 6 weeks old go through nights with no supplemental heat with the lows in the mid 20’s.
If yours have been kept in tropical conditions, they are not used to cold weather. Even then at seven weeks I’d expect them to do OK in the temperatures you mentioned, but if you can do it without burning the coop down, heat one corner and watch them. As long as they have room to get away from the heat if it is too warm, they will do fine. They will position themselves where they are comfortable. If that is as far from the light as they can get, turn the darn thing off.
