Strange. If your eggs are hatching in the daytime, you may need to steal the rock with eggs in the morning. This is unusual, though, but it's possible yours were just ready to hatch, and so did. If you cannot take the rock out, you'll have to stand by to catch them with a bowl, but it's likely that the parents or other fish in the tank will get them all before you do.
Another explanation is that the eggs became non-viable and died, therefore falling off the rock. If the eggs turn white, they've died. If they stay silver with the silver eyes, they're still good. Healthy eggs can withstand a lot of water pressure against them. If they fall off with the blow of a turkey baster, they're bad.
The only other reason I can think of is that the male decided to eat them. Make sure your parent clowns are well fed with a good variety of different foods.