Mine are candled at day 7 or 10. That will give you a chance to toss the clears or the ones with blood rings. No use having your hen sit on eggs that aren't going to hatch.
Also you should mark your eggs so you know which ones are supposed to be in the nest. My broody stole an egg from a different nest box yesterday, and another hen has laid an egg in her box 3 times. The new eggs should be removed (daily) since they are not going to hatch with the others anyway. I also candle again at day 14 or 16 and toss any that aren't developed. Bad eggs can also rot and explode on the healthy ones, so it is a good idea to get rid of them.
Also you should mark your eggs so you know which ones are supposed to be in the nest. My broody stole an egg from a different nest box yesterday, and another hen has laid an egg in her box 3 times. The new eggs should be removed (daily) since they are not going to hatch with the others anyway. I also candle again at day 14 or 16 and toss any that aren't developed. Bad eggs can also rot and explode on the healthy ones, so it is a good idea to get rid of them.