The eggs really are not in a sack. They are embedded in a matrix cement.
Stomatopod females can store sperm for several months provided they have not molted.
If the eggs are fertile, they will hatch in a couple of weeks, the larvae will stay with the female for 3 or 4 days, and then they will enter the plankton. If they were not fertilized, she will eat them in a few days.
No one has ever reared larval Odontodactylids, so don't worry about it.
Roy