tele_mark says:
There was a 50F day here last week where I was able to open the door and let them out for a little while. After 6 months inside, all they did was stay outside for about 10 minutes and go back inside! Then I modified the old basement window door from the old house to fit in the bedroom window, and jury-rigged a ramp outside, and found it works pretty good. So eventually they'll be able to go out as they please, especially after the rear door is replaced with a slider.