Just move the rock into a down tank.  As Neil said the eggs are quite resilient to water change. 
 
Depending on the clowns, most will hatch the 8th night of spawn.  About 2 hours after lights out. 
 
I have found you get a better hatch rate when the tank is pitch black with no light at all. 
		
	
		
		
		
		
			
		
		
		
		
	
		
		
	
	
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