Pesachim 4 - Why search for chametz so early?
Now that we agree that the "light" of the search for chametz is night , it is valid to ask why it must be done so early. Even if we are trying to rush to do a mitzvah, we don’t find anywhere that it should happen the night before. Since chametz will be only prohibited from the middle of the next day, we could require the search to be done early in the morning.
Rav Nachman answered that there are two reasons for that: first, people are usually found at home at this time, so albeit a little early, but guaranteed that all will take part. Also, we really want to use a candle, and night is best for that.
If one rents a house around the fourteenth, who is supposed to search the house for chametz, the renter (because it's his house) or the house owner (because it's his chametz)? For the mezuzah, it is the renter’s obligation, but that is because mezuzah is for the one who lives in the house, not for the house itself. For chametz, it is exactly our question, is it for the person or for the house? Again, Rav Nachman quoted a rule that resolves this: if the renter got the keys before the evening of the fourteenth, it’s his obligation, and if later - it’s the house owner’s.
The Talmud also considers the situation where the renter assumed the house to be checked and found that it wasn’t - can he ask for his money back.
Art: The Keys by Edmund Blair Blair Leighton 1853 - 1922