Switching from growers to layers

My Speckledies are 16 weeks old and in theory should start laying in a
few weeks time. When should I be switching from growers to layers? I
don't want to start them too early as they will still be growing.
Are they likely to start laying later at this time of year due to the
lack of daylight? or are hybrids not so fussed about the weather?
TIA
Bryann