Ok so I have a couple khakis that are about 3.5 weeks old. They have been living outside for the past week in their small cage. I have not used a heat lamp on them and they are doing really well. They are not completely feathered but they are starting to come in. And they are still pretty small. When would be the best age/time to put them in the big pen? The pen is only a 10x10 so it's not huge.