When Can I Start Putting Training Eggs in the Nest Boxes?

I have 4 nests and have had up to 18 layers...worked fine, not that there weren't some squabbles at times.
New layers may lay anywhere at first.
Curtains are for the keepers more than the chickens.

 

I put wooden eggs , not only to show them where to lay, but to solve the problem of all the hens that want to use the same nest even if there is a hen in that one already. This morning two large gals were trying to crowd into one nest box. I have 5 very nice nests, go figure. So the wooden eggs will go in again for a while. Plus my new ones, just at POL are using the floor, so it is egg hunt every morning. Where are their brains, oh that's right, tiny brain.

 

I mainly use my eggs now to just help solve disputes.