Bielefelder normally lay all winter without light programm as long as they have a coop with a window / roofed run and don't sit all day in the dark. On winter solstice we have 7 1/2 hours day light but winter skys here are often heavy clouded and that can slow down the egg production or/and color of eggs. Like with most birds sudden temperatur drops are a reason to stop laying.
Most hens begin between 28 and 32 week, but you can have extrem late starters. Earliest was a hen that lay a small test-egg with 6 month, then stopped and restared three weeks later. Latest was a hen that hatched in late June and started laying in April, but I think that was a case of an extrem bully victim. She began to lay after she was rehomed.
If you want to monitor the hens for production abilities I would begin with the check of the egg-gap of the pubic bone and note when the gap begins to widen, b/c I often thought I knew who layed an egg but some of my hens really tricked me by sitting on a nest with an egg from an other hen and singing as if she had layed. After checking the egg-gap I realized that some of my young hens like to practice sitting and singing. I know my Barbus are a strange breed, but I think most poullets are interessed in nest boxes, nest building, sitting in the boxes and singing way before they start to lay the first egg.
Bine thank you so much for that valuable first hand information. I hope it is an encouragement for anyone who's pullets are close to that age but not yet laying. Its good to know that 28-32 weeks is not uncommon for the German Bielefelders to lay their first egg and that you can experience as much as three weeks gap between first egg and the full laying cycle to start. This lets us set realistic expectations for our Bielefelders in America.