How long should you leave eggs in box for hens to set?

Chickens don't lay their eggs in boxes for you to put back. A hen will decide she is ready to hatch a brood of chicks based on the amount of daylight hours (12 hours or less signals time to start laying eggs and begin nesting) and suitable nesting and food source. Once ready, the hen will find a secluded place to lay her eggs, which can be anywhere in your yard or home (they LOVE hay bales and barns - but also under bushes, in flower pots, in the mulch, etc). She will sit on these for about 3 weeks before chicks hatch.