I wait until the first pips then cut the rest to se what they are and what not. I had one pip and didn't make it cut large enough and was all caught up on th egg shell and could not pull all way back in ( was fun tring to cut out a snake lol.) I end up cutting a larger ring around the snake and then slowly worked my way up to the slit area.to free it.
Now I had one snake cut the top and bottem of it egg in the same day it was a trip cause it went from plumb and ok looking ot ossing mess as the remaining fluid drain out I wait at least till the day before they due to hatch (example) due to hatch june 21 then I may cut about the 20th if ican wait that long.