It's a lovely thread to read. Young hen are like fine girl. .
I leave my young hen of any species in full view of the cock. Like men they drew over young girl.
they sing and eventually feed her.
It hard to know when they are born; it takes around 15 months to mature before introducing together in cage. It's even better if she is place with a older hen same spicies or granny canary(a great teacher). By 15 months;The young bird is no longer a girl but a fine lady. She is at her best peak to breed really quality birds. She will be no longer shy if approach by male counter part.
That why in canary world this rule don't apply:- i find first round hen some of them too young get misunderstanding if older cock are in ,lay egg on the ground ,build nest roughly or when hatch sit to tightly in the nest killing all chic.
I apply this rule to all my finches.
Quality is always better than quantity.
Don't crack under pressure.