well "lock down" is day 18 thru hatch....the mama hens will not get off the nest in order to keep the eggs moist and warm. so during artificial incubation someone made up a rule that on day 18 you no longer open the incubator....it's really to keep newbies from over zealously candling and fiddling with the eggs causing them to dry out....
that all being said...it's a good rule...if you don't know what your looking at, what's normal or abnormal, it's best to leave the hatching eggs be.
especially once they externally pip please refrain from opening the bator....if that inner membrane dries it is just awful for the chick!! add a blob of wet paper towel quickly if you need the humidity higher
Thanks so much for the info. I see that some do lockdown at day 18 and other folks do it at day 19 or when they see the internal pip. Either way seems to be OK. I will make sure to NOT open the incubator during lockdown. This is why I bought the Brinsea Octagon 20 for hatching only 9 eggs, so they would have lots of room to hatch, and more enjoyment for me to watch! I had the smaller Mini Advance for my first hatch and didn't enjoy watching the crowded hatch and they could barely stand up in it.
This board is the greatest!