Corys fertilize the eggs as they lay them, so waiting for them to be fertilized later isn't an issue. If you ever get to see it, it's really cool. They swim in a "t" formation, with the female's mouth at the male's vent to collect the sperm in her mouth. She carries a single egg at a time in her pectoral fins, and places that somewhere, then "spits" the sperm out on to it.