Hello

I've got my very first clutch of eggs about to hatch and I'm not sure what to do. I'm at day 57 and only one eggs has started to shrink in. My humility has been perfect along with a slight variation in temperature but it always stayed between 87 and 89. My question is, how far do you push it before you intervene? I've seen way to many horror stories of people cutting, it's being to early and the babies dieing. That being said I dont want to wait to long and miss an opportunity to save a drowning snakes life. My thoughts are seeing as how only one egg has started to shrink that they just arent ready yet. I'm of the mind to let nature take its course but what do you think? Is there such a thing as eggs just not shrinking and still hatching?