I have three nest boxes between six hens. Four of the hens are 17 weeks old and two are 10 weeks old. I started out with all of the nest boxes available for use and some of the older birds would sleep in them and make a mess in them. So I covered them up with cardboard. That was about three weeks ago. I am wondering if it is time to uncover them and give them another shot of using them for only their intender purpose or should I leave them covered until I find an egg on the ground in the pen? As you can tell, this is my first flock of chickens, so all is new to me.