I don't know where you live, with main interest being how soon your days start to get reasonably longer. Even if I knew where you were, I would not be able to give you a good answer. I'm not that good and chickens are very individual. Commercial laying operations keep the pullets on a restricted light until they get old enough to lay a decent sized egg. Then they will increase the light and they start laying. So I would really not expect yours to start until the days get noticeably longer. But pullets can be hard to predict. Older hens are more reliable.
In your case, I would open the nests up with fake eggs in them at about 16 weeks age. Chickens don't always read the rule book very well and even when they do, they get confused very easily. Or maybe they just don't like to follow the rules. It is possible they will start laying that young and you want the nests ready fro them so they get in the habit of laying in them instead of somewhere else. I really don't expect yours to start that young, but I like to know whether there are any problems while you still have time to fix the problem before they start laying. The type of problems I'd be looking for are them sleeping in the nests or the lip on your nest not being high enough and they scratch out the bedding and fake egg.
Hope this helps. Good luck!