chicks hatching day 18 why ?

[bigdawg]

i have one silkie chick hatched another has pipped. i am using an egg-o-meter from icubator wharehouse. temp has been steady 99.5. forced air. hova bator. the oldest egg was 10 days old. started with 15 and 14 went to lockdown very late on day 17. when i started collecting the eggs i put them straight on the turner. temp stayed around 60-65. bator was preset prior to putting eggs in. last egg went in i filled water tays and plugged it in. my cheapo walmart thermomter/ hydrometer thing said temp was around 100 to 101.0 not dependable. always read higher with other hatches and compared to other thermometers. now any ideas why there hatching early.

 

[Bock_Bock]

i have had the same thing happen before, it could be your temp even tho you said it was holding preatty steadily it coulda had a temp spike somewhere, another is if this is a bantam they tend to hatch earlier then standards some time, there is alot of reason to be truthful another is the chick just might of gotten to big for the egg and the only room it had was to pip the air sack and in doing so it just didnt stop there it went all the way, or maybe when you collected the egg there was a hen that got cozzy on these eggs and started the incubation attempt early before you knew it when you collected them in the first place