Pesachim 4: Who's Who - Rabbi Hiya. Another example of using euphemism for more refined speech. Also, everyone agrees that "Or le-14" means the evening, but why the evening? Possibly because we have zeal to do mitzvot at the first possible moment. But that principle usually means the morning. But people are at home at night. And you get that pinpoint light in the dark. Also - how reliable are the people who claim a house has been checked for chametz? What if that person is a woman? A slave? A minor? Depending on your presumption of the right thing having been done, you can surely rely on them! But what if there's no presumption that the house has been checked, and we need to rely on their statement?