They should be feathered enough at 7 weeks; some on here will say 8 weeks, but not much difference. Remember they are just as likely to hide in a corner out of fear as being cold. Chickens are "chicken," afraid of their own shadows. Many find it takes them a week or more to even go into a secure run, in setups where it is separate from the coop.
Now, 3 weeks old in 60's weather without heat might be pushing it -- but some on here do this without a hitch, as well, and that poster said they were content. Some on here feel the chicks feather out faster and are hardier if kept cooler. I try to keep them at the cooler end of the spectrum when raising them; I think we tend to overheat them, making them lethargic, and dehydrating them. And I will never brood indoors again.