Whan about half of the eggs go silver then they are likely to hatch that night. Ocean Aquatics sells rotifers so you might want to check them out.
If you put the rock in the other tank place the eggs in a position so that the airstone is still making the eggs rock and if you leave the eggs in with the parents then be prepared to stay up for a while that night with the pumps off and a flashlight at the surface of the water. I think they should hatch within a couple of hours after lights out. There is a little bit about hatching at
http://www.aquarium-design.com./clownfish.html If you can't get rotifers in time then I have heard of people trying ground up spirulina flakes with some success.