Or HaChaim on Genesis 19:4/אור החיים על בראשית י״ט:ד׳

1 טרם ישכבו, Before they went to sleep. The Torah is careful not to write: "after they had eaten, etc." From this we learn that something transpired between Lot and the angels after the time they completed the meal and before their retiring for the night. Our sages in Bereshit Rabbah 50,5 mention that when questioned about the townspeople by the angels Lot said that whereas all over the world there are both good and wicked people in a town, in Sodom the people were mostly wicked. We have previously explained why the angels did not immediately destroy the town when they heard this. Besides, according to the Midrash, Lot asked them to spare the city and they accepted his plea. It was only after they were about to add further sins (verse 5) to their already full register that the angels told Lot to save himself and his relatives (verse 12) prior to their destroying the city. There was an additional reason why the angels did not immediately destroy the town. They waited till morning, a period when the attribute of Mercy is in the ascendancy; at that time they would succeed in saving Lot. They could not have done this during the night. Our sages add that since the Sodomites worshipped both sun and moon they were smitten at a time when the moon is full (middle of the month) and the sun shone, to show that neither force protected them.