שמות יב:כט פירוש: רש״י, ספורנו, רשב״ם ורבנו בחיי

וה׳ “AND” THE LORD — Wherever it is stated וה׳ “And the Lord” it signifies He and His celestial Court, because the prefix ו expresses an addition, just as one says, “Mr. So-and-so and Mr. So-and-so” (Genesis Rabbah 51:2; cf. Rashi on Genesis 19:24).

וה' הכה, while the Jews were busy with preparing and eating the Passover offering, G’d was busy with killing the firstborn of Egypt and orchestrating the redemption of His people.

בחצי הלילה, while they were eating their Passover offering.