That is the reason hens stop laying in winter - lack of light, although I do not like lights on after dusk. Although not on as big a scale, I have relied on hens for my income from time to time over the last 60+ years. They need to be dry and not in a draught. Never experienced worse than about -25ºC (about -13ºF) outside and never found the need for heat. Also 45ºC (113F) or so in Australia, and that is worse
The reasosn for bringing lights on early is that almost all of the eggs will be laid in the first 7hrs after "lights on" so there are constantly hens going into the boxes and the eggs do not freeze before they are collected. In northern Scotland it was Midnight to 4 p.m. in mid winter - free range. Where I am now it is getting to be just after 3 p.m. when the sun sets so I would have needed to switch off by about 2.30 p.m.
Never subject the hens to 24hrs light. They need their rest the same as every other living creature.