The first few times they lay eggs, they may either eat them or they are not fertilized. They are getting used to the process. As they get better at it, the nests will get larger. I would say to wait a bit before attempting to raise them. Mine still eat them every once and awhile. They get bad batches (eggs turn white), and I just chalk it up to nature.
As for hatch time, it's based on type of clown and temperature. Ocellaris normally average 6-9 days. I keep mine at 80 degrees, and they hatch 7 days after being layed. They lay eggs every 11 days. To tell if they are going to hatch, the eggs go through a color change. They start out orange, till they get to silver. When you can see the eyes reflect the light, and the egg is silver, they wil most likely hatch that night. Normally 1 hour after lights out the hatching starts.