The experts estimate standard hatching time for chicken eggs at three weeks. From the time you place them in the cabinet incubator, you can start counting 21 days. Once the time for hatching comes, consider moving the eggs to the bottom hatching tray if your unit is equipped with one. Not all eggs will hatch after exactly 21 days. Some will take a day or two more, and that is okay. However, if the eggs take more than 23 days to develop, it might result in unhealthy or weak chickens. That is why professionals recommend stopping incubating several days after the three-week period.