What kind of incubator are you using? I recently discovered that the temperature my incubator's digital readout was showing was actually about 2 degrees above what the actual temperature was. I had a lot of eggs that I paid a lot of money for NOT hatch as a result. They grew, slowly, then just kinda petered out at the end in lockdown. I don't think they were mature enough yet or something, but it happened twice before we decided to put a freshly-calibrated digital hygrometer/thermometer in the unit and test the temp & humidity. I thought I was incubating these eggs at 99 degrees, and it was right around 97 the whole time. I thought the humidity was up to 60% at lockdown, and it was actually maybe about 40%. Bad on me for not putting in a separate hygrometer/thermometer (i.e., I ignored everybody's advice... seriously, listen to the long-timers here, they know of which they speak). Now we are having a good incubation period in that bator. We candled last night, day 13, and out of 32 eggs originally in there, we still have 27 (had already taken 2 out on day 5 because they were completely not developing). That's a LOT better rate than the last clutch of eggs we hatched in this unit. Out of 16 eggs, we had 3 hatch. Two of those had not fully absorbed their yolk at hatch and died within 4 days of hatching. The third, a barnevelder, is healthy and spunky. So we had 1 healthy egg hatch out of 16 due to low temps, and that was a *real* expensive experiment.
My point is (didn't mean to hijack your thread) to make sure you get a separate thermometer/hygrometer and calibrate it, then put that in your incubator to confirm the accuracy of your current readings. It takes some time and a couple of failed hatches to get it down, so don't beat yourself up too badly (easier said than done... just don't let yourself get discouraged while you're going through the learning process).
Your chicks may still hatch, even though it's day 24. If you still have nothing on day 25, do another float test to see if they're still alive, or peep at them and listen to see if they peep back.
Here's sending you good hatching vibes and wishing you all the best!
