Depending on the temp of your tank, they can take about 48 hours to hatch. First they will hardly be noticeable as wigglers and the parents will move them around if you bother them too much by constantly looking in the tank or hover around the tank. When you feed the parents, they will feed the wigglers. They sift the food through their gills so that it's smaller for the fry. They will continue this once the fry are free swimming as well. You can also supplement with frozen baby brine shrimp, frozen daphnia or Hikari First Bites if you plan to move the fry into a grow out tank. Keep the parents well feed and any other fish that are in the tank. Do small, frequent water changes so that your water parameters stay in good condition.
As for how many there will be, that depends on many things. If they were all fertilized, if the parents eat them, which happens a lot with the first few spawns. If they get fungus. If the other fish in the tank eat them. My spawns usually yield about 50-60 that I can trade/sell.
