Somewhere in my travels I came up with 180 days. My husband and I both remember that this has held true for all of the birds that we have had - but I think we are both getting senile because I can't remember where I got this info from - seems like it could have been an old (older than us) farmer. But I cannot find this number anywhere on the internet.
Since I now have a small flock of 4 different breeds it will be interesting to see if this still holds true with them - if they do lay at 180 days it will be November before we get an egg and then the days are getting so short that they probably won't be very productive.
You can leave a light on them but a farmer I am currently buying eggs from tells me that this shortens thier life span - so I think I'll just let nature take it's
course.