Actually, without all the sarcasm, it's true. Most rocks and debris comes from freight trucks which are more predominant during the day. Not to mention all the guys that haul stuff personally (usually not having it covered correctly hence leading to small things coming out at highway speeds) are also during the day. You'll get the occasional car flinging one but it's mostly the trucks. You can disagree if you want, I go by experience. Besides I know the covers aren't usable during the night and don't feel like endangering anyone by using them, that's just plain ol' dumb.