Hi there - my earliest started at about 18 weeks, but that is unusual.
A lot of Marans, especially the French varieties will take longer, and 26 weeks at this time of year is certainly not unusual.
I think, as well, late hatched pullets take longer to mature, so its a bit "how long is a piece of string". But I do find that Christmas is normally a turning point for pretty well all my birds. They seem to be up and about. Mine are up by around by 8 - 8.30 ish and thinking of bed at 3.30 ish so maybe its a bit lighter here than with you?
It takes around 26 hours to make an egg and I have read somewhere it is not the hours of daylight that makes the difference, but the fact that the birds are not eating enough to make an egg. ie 6 hours of eating and 18 hours of fasting, so apparently, though I have not tried, it is best to light them half way through the night so they can get up and eat then go back to sleep, but that would need a dimmer, otherwise they would not find their way to the perches.