It sounds like the hens get to run freely to some degree since they have access to your and your neighbor's window sills. Are you certain that they haven't been laying somewhere unexpected? My first layers were laying under the coop right on the dirt for example rather than in the nesting boxes. There's plenty of stories I've read here on BYC of hens laying in tall grass, under bushes, in crawl spaces, in or under out buildings/sheds, etc. I personally keep my hens in an oversized run around their keep nearly always, so the number of places they can lay is limited. If you cannot keep them confined to a run, I suggest keeping them confined to the coop for a day or two to see if they are laying. Also, have you placed ceramic eggs in your nesting boxes yet? Hens lay where other hens lay as they feel it's safe there if another hen laid there. Ceramic eggs (feed stores sell them) are a proven decoy to trick hens to lay where you want them to.
Now if they truly are not laying at all yet, I agree with some of the other feedback above. Environmental conditions and genetics play a large role in when hens will begin to lay from what I have gathered. Additionally, food is thought to play a significant role. Are you offering a source of calcium yet? I use roasted egg shells (repurposed) and crushed oyster shells (feed store sells these by the bag). What are you feeding the hens - have you switched to layer feed? Layer feed support egg development (high protein, calcium, and other nutrients required). I go as far as fermenting my feed and offering scratch and vegetation (mostly weeds from the garden). Not that it's necessary, but I feel the added nutrients and natural foraging keeps the hens healthy and happy. Lastly, are the hens stressed for some reason? Being cramped into a small coop, poor diet, animals like cats and dogs regularly frightening them, and overly aggressive roo or other hen... all of these could stress a hen, and a stressed hen is not likely to lay as well. Keeping them healthy and happy is the best way to get them to lay.