Chickens require 14 hours of light daily for optimal egg production.
There can be not much difference in optimal egg production and what you actually get. That 14 hours is what commercial operations do but there are other factors besides length of light. They want each hen to eat just enough for optimum egg productions but not any more. When they wake up hungry they automatically feed a certain amount of feed so they all are busy eating and the bullies are not keeping the weaker ones away so they all get to eat. When they are hungry again they dump some more feed. They don't want to do this when most are on the nests laying so they have those intervals timed. They have worked out a system where 14 hours gives optimal egg production but there are other factors than just length of light.
In Arkansas with less than 10 hours of light in the depths of winter I had pullets that were laying an egg 5 to 6 days a week. I had hens that had finished the molt and started laying when they finished in December, again laying really well. Production was not as good as in the better months but it was totally respectable. Production would really drop in severe cold, but it also drops in severe heat in summer.
I think the real problem is the molt, especially for those younger ones. I expect those Australorp especially to come back gangbusters well before the day length reaches 12 hours, let alone 14.