You can go quite a while without light, imaging a multi-day storm in nature. 
 
If you bulb is coming in a couple days dont worry about it.  If you want light for your fishies to see by, that might be a good idea, use a work light or trouble light or anything else handy. 
		
	
		
		
		
		
			
		
		
		
		
	
		
		
	
	
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