Low Quantity (1 quart) in Differential

first, no i don't think you hurt anything. Second our trucks are as smketter said are 1/2 below the hole. I am not sure how you are supposed to measure such a thing but i lay my last knuckle of my little finger in the hole and bend it down...it comes out about half covered in oil. others are filling level with the hole...which likely doesn't hurt anything either.

Either way make sure the stuck is sitting level. it will make more difference than you think.