A math formula I suppose.

[MorphMaster]

Just guessing that the op is asking about 55 days for avg. incubation period.

Ya that's why. I could've said 52 days for minimum or 60 for the usual max but it was just a rough number. But what I mean is how do you figure out the specific date

[snakesRkewl]

There is no specific date, they are ready when they are ready.
52 days until a head pips is my normal but I have had pippers at 51 days and at 56 days and everything in between.