You can candle them before you incubate to look for hair line cracks, detached air saks. After that candle them around 7-10 days and then again around day 14 or 15. You could candle earlier but sometimes it is hard to tell. If the eggs are dark colored or blue or green it will be hard to see in them, make sure you have a BRIGHT flashlight. This schedule is not set in stone (it just works best for me). Good luck with the eggs!!!