The rendering of time for the Hebrews was that a day began at sunset and ended at sunset. Historically, at the beginning of the 15th of Nisan in Ancient Egypt, the Jewish people were enslaved to Pharaoh. After the struck Egypt at midnight, killing all the first-born sons from the first-born of Pharaoh to the first-born of the lowest Egyptian to all the first-born of the livestock in the land (Exodus 12:29), Pharaoh let the Hebrew nation go, effectively making them free people for the second half of the night.