People often ask if their egg clutches are fertile so here is an example of an infertile clutch (left) next to a fertile clutch (right).
These two clutches were laid within 2 days of each other. The one on the left is “bad” or mostly if not completely infertile. See how the egg cells are small and not very bubble like? Two other tips on detection: 1) smell a clutch that you suspect is bad if it’s been at least two weeks. Infertile or bad clutches have a distinctive smell while healthy/fertile clutches do not. If the clutches are sitting on a damp paper towel, do you see a red/pink stain under one? Only infertile clutches will stain the paper towel. You can see in the photo above that the left clutch has stained the paper towel pink underneath it.
The one on the right is very fertile and it will likely hatch In the next day or two. It would still be necessary to wait a week to 10 days to be able to tell this as egg development is unclear until that much time has passed. About 3 days before hatching, a fertile clutch will start to change color to look moldy prior to hatch. You cane see the color changes in the Mystery Snail Egg Development page link below. It takes anywhere from 10 days to 4 weeks for an egg clutch to hatch based on temperature and other conditions.
Florida Mystery Snails 