I have read in books and on here, that by 3 weeks they can regulate their own temps. i would think by 7 weeks they should be well feathered. Are they?
I did read that you start new chicks off at 95 deg under heat lamps and each week lower the temps by 5 degrees. So at 7 weeks I would think they wouldn't need heat lamps anymore. but would need natural light, like from the sun.....maybe keep them by a window?
you should put them out for a few hours and just make sure your monitoring them. if they have a bad reaction to the weather bring them back inside. i doubt that will be a problem, they should be fully feathered. at about that age,they can maintain theyre own body heat