01
Source and decoding
והשתא דקיימא לן דלכולי עלמא ״אור״ אורתא הוא, מכדי בין לרבי יהודה ובין לרבי מאיר — חמץ אינו אסור אלא משש שעות ולמעלה, ונבדוק בשית
Now that all agree that or means evening: according to both Rabbi Yehuda and Rabbi Meir the Torah prohibition of chametz begins after six daytime hours have elapsed, so let us search then.
The Gemara asks why we search at night if the Torah prohibition begins after six daytime hours. It considers that one might search in the morning because the zealous hasten to mitzvot, but Rav Nachman bar Yitzchak explains why the search is nevertheless held at night. Rav Nachman bar Yitzchak answers that night is when people are at home and candlelight is good for searching. Abaye adds advice that a scholar should not begin studying at the hour near the search, lest he miss the mitzvah.