It's never safe to cut into a egg prior to the first hatchling pipping. There are so many things that can go wrong. It's a 60 day incubation for a reason even though most hatchlings emerge prior to 60 days based on incubation temps and internal egg genetic problems. Simple mold can safely be sprinkled with antifungal powder though. Day 55 seems to be the consensus if cutting is the only alternative without seeing pipping of the siblings.