When should I be offering poster shell?

[Stoney Meadow Maple]

We have 4 hens at 3.5 mos and our new runners hens are 1+ years. The runners have shown no inclination to lay yet, as they are pretty shaken up by the move I am not really surprised. Should I be offering oysters just in case? Do I need to worry if the younger ones are eating them or if the drake does? How much should I put out? A cup? A gallon?

 

[AllenK RGV]

I have offered it in a separate dish, broadcast in the driveway. My hens don't show interest in it. After point of lay is the general consensus on when to offer it.