From everything I've seen and read so far, once they are fully feathered, they should be good to go outside. You'll definitely want to put them out now, too. With the slightly warmer weather this weekend, it will allow them to get better acclimated to the cold and you won't have to keep them inside all winter. My girls are about 9 weeks right now and have been outside for the last month or so. They are perfectly content and are doing great. No severe huddling, no shivering, or anything. They are plumping up quite nicely and have grown some beautiful feathers! Now I wish I had some recent photos to post!
Oh, and we've been hitting between the high-30s to the low-40s the last month at night, so it's been a touch cool at night. I had to break out my leather jacket and riding pants to come home from work every morning. Winter is quickly approaching!