When should I give layer pellets?

My girls are still all on growers pellets, as none of them are laying yet. My oldest 2 hens are around 24 weeks old (both bantams, Pekin and Wyandotte) , my youngest 2 are almost 13 weeks old and the other 2 are 16/17 weeks old. I still have half a bag of growers feed left, so should I continue with it until the first egg arrives? When the big girls start to lay will the little ones be ok on layers too?

I have attached (hopefully) pics, one showing my 'not so bright' lavender Araucana in the  flower pot of my lavender bush, that she uses as her personal dust bath! We think she looks like 'Buckbeak' the hippogriff in Harry Potter.

oh bless I love that second piccie, looks like they're all lining up for a square dance and bowing to their partners