They can lay anytime after day 25 from Pre Lay Shed but 30 days is an average. My daughter's went on day 27. I have seen others on here that didn't go until 40+ days. You just have to watch and be patient. As far as weighing them, we just used one of those small disposable Glad container and zero'd out the scale. The eggs didn't stick to it. They are only going to be contacting the surface for less than a minute to get an accrate measurement.