I would like to re-iterate that adding light in the morning is better than in the evening.
Be aware that with some flocks, the addition of light can make them uneasy and they may start to peck at eachother. This problem is seen more often with evening light, but happens with morning light also.
Also think of the fact that hens do need some "time off" to do things like help replenish calcium to bones, as well as other nutrients. THe lack of light also helps the hens' body know it's time to molt. Molting is an important process, but you don't want them to begin moulting when it's freezing outside (especially if they end up in a hard moult) .
I noticed that the hens that I allowed to hatch young, layed later in the year and also layed more consistantly after "their break" than the others (I keep track of each hens' laying daily).....which just strenghthens my thought that breaks are important. Remember, factory chickens don't need a break, because the factory just gets rid of them after 1-2 years....Us backyard chickeners keep chickens for their lifetime--so a break is warranted.
If living in the far north- adding light to continue laying can be a good thing--especially since the winters are so long, but I recommend making sure they get at least a little bit of time off each year.
Sandra