Once you have incubated several clutches at the same exact temp it will give you an idea on when your snakes will pip out, if you ask different people there will likely be a difference of a few days even if they incubate at the same temp.

Egg shape is variable as well I have had eggs completely dimpled when the first animal pips out and some that are still nice and plump when they did.

I incubate at 88.5 degrees and my hatchlings usually pip at day 60/61 and emerge out of their eggs 2 days later.