You can candle any time you want, but if the eggs are dark colored, or if you don't have a strong enough light, you won't see much of anything until day 7-10. I usually candle around day 7, then again day 10 or 14. That way you have a comparison, and can tell if there is any change. On day 3, you might be able to see the veining somewhat, but it would be hard to tell. And do not toss the eggs until at least day 14, unless they are stinky or weepy!! And if you are still in doubt, wait till day 18, by then the whole egg will be dark, except for the air sac. If this is not the case on day 18, then toss away! Good luck!
I'm the odd-ball on this forum - I candle every night. I can tell at day one if the blue and green eggs are fertile but can't tell till about day 3 if the brown eggs are fertile. I can easily see into the blue/green eggs but my brown eggs have shells that are so speckled that it's like looking through sandpaper. I love watching them from day one all the way through hatch. It's my chick-n-egg T.V.
I know there are those who say yada yada yada about not opening bator and the humidity and the temp yada yada yada but I've never had a problem - never lost a chick. And now that I'm hatching my own chickens' eggs, they are always fertile and I've rarely had one start to develop and then stop - only had that happen with eggs I find in hidden nests and don't know how old they are so I throw them in bator. I also open the bator and take the chick out the minute it hatches because I always have a bator full of eggs that range from day one to day 21 and I don't want a new hatchling to go thrashing around and bumping eggs together. Again, never had a problem.
Then I go and put them outside with all ages of chicks/ducks/peacocks and let them start free ranging at 1 week old - yep, no problems, no losses.
So, moral of the story - go ahead - break the rules - peek in on them whenever you want.
However, I just bought a new Sportsman incubator this week and loaded it up with several trays of eggs so there goes my nightly "egg check" - just too many to do now and too difficult to get them out of bator which is outside in stable tack room. Guess I'm gonna have to keep my little styrofoam, basic model, HovaBator in my bathroom with eggs in it or I'll miss my nightly egg-check and chick hatch. It really is cool to see them progress and hatch.
Ruth, I'm with you... I usually don't even try until day 4-5, though, but I've heard that it's good to open the incubator, let in fresh air, let them actually cool a little (just like a hen getting off the nest to eat). I will usually take a penlight and just run it across the top quickly, so the incubator isn't open for more than 5 minutes, but I figure if the hen can get off for 15-30 minutes without ill effects, why not? I for sure candle just before moving them to the hatcher just so I'm not setting clears.
But, I also agree, don't toss any eggs until day 14-18 unless you are ABSOLUTELY sure of what you're looking at. I've seen some eggs that I thought were rotten, only to have them hatch.
You're right about the momma getting off the nest. I have two broody hens and a broody duck right now and I watch them get off the nest at least twice a day and go take a walk, eat/drink, or just sit off to the side.
I can't imagine not opening it for 21 days - it would be like an Easy-Bake oven and I would imagine some embryos would just get cooked. Like I said, I open it during the day/night, sometimes many times, if only for a minute, to get a hatching chick out; turn the eggs; add eggs; candle eggs and I have 99-100% hatch rate on fertile eggs running staggered hatches with chicken and sometimes duck eggs at same time.
I try to do it all the natural way. Same reason I don't leave baby chicks in a closed brooder box under heat lamps for weeks on end - they too need fresh air and sunshine. Never, ever lost a chick.
So Kelley - have fun with the hatching - have fun with the new baby chicks.