It is not clear whether you are referring to eggs or larvae. Eggs will take from 12 to 21 days to hatch depending on the species. Once they hatch, their fate will again depend on the species. Gonodactlus larvae will remain with the mother for another week, molt three times and then enter the plankton where they will stare to death in a couple of days. It is nearly impossible to rear them without very specialized facilitiies and the proper live food.
Roy