How long do I wait?

[New to This]

We candled the 12 eggs in the incubator on days 7 and 14, and they were growing nicely. Now it is day 23 and the chicks are not hatching. How long do I wait? I don't want to get rid of them too soon. And why, if indeed none of them are going to hatch, did they not? We checked the humidity, ventilation, and temperature, and they were all correct. This is our first time hatching chickens, so any input is greatly appreciated! I'm going to have four devastated little kids here if this goes poorly, which I'm afraid it already has...

 

[fried green eggs]

I'm kind of new to hatching but, have had 3 pretty successful ones so far in my 2 home-made incubators. I candle them again on Day 18 just before putting in lock-down. On my first hatch my chicks started hatching a day early - I discovered my new digital thermostat/hygrometer with probe is not accurate so, warmer than I thought. Now I use 3-4 thermometers and at least 2 hygrometers in each incubator. No pips at all? This doesn't sound good sometimes they are hard to see b/c they don't break a hole in shell. At this point - I would preheat & up the temp in your bathroom and raise humidity level with hot steamy water and very quickly pull eggs and close incubator back up to candle them in the bathroom. See if you can see any movement or hear any movement or if you have a cheap stethoscope you can make out a heart beat. Maybe your thermometer &/or hygrometer is not reading correctly. If, it is lower than you thought temp was while incubating - I have read then eggs can hatch late