My chickies are only 10 weeks old this week so I know they don't need it yet but I'm still confused on oyster shell. I know they won't need it for at least another 6+ weeks but is it better to give it to them as an "insurance policy" type thing or wait until they need it? What age should I start introducing it? Just before they start laying? How do I know if they're getting enough? Do you throw it on the ground or put it in a bowl like I have my grit? Also what age should I unblock the nesting boxes or should I wait until they start laying?