I am in the learning stages on this one also. Now that I am getting a feel for the sizes of healthy hatchlings.. based on this, I would slit if I thought that the hatchling was pretty small and might not be stong enough to get out of the egg. I am on day 57 with Ginger's clutch and I see no reason to slit now. Each egg holds a baby, and I can see them through candling. I don't care to know whether or not they are morphs at this stage. I just want them to hatch!
It is personal preference I guess. From the posts I made, people's advice ran the gamut from "I slit at day 51" to "Slitting is bad; let them come ot on their own and if they don't, they probably aren't healthy anyway.) These replies were from another forum (KS.)