My chickens are probably about 4 to 6 weeks away from laying. I am wondering if when they get close to 20 weeks and have not started laying yet, is it okay to introduce the oyster shell at that point, so that their first eggs will be harder and perhaps avoid the mis-shapeness that first eggs can have? Also... when I do start giving the oyster mash... how much do I give 11 chickens. Do I mix it in their food or throw it out like scratch? thanks