They forgot to mention this passage from the Torah.
Exodus 11:4
“And Moses said, Thus saith the LORD, About midnight will I go out into the midst of Egypt”
And later...
Exodus 12:29
“At midnight the LORD struck down all the firstborn in Egypt, from the firstborn of Pharaoh, who sat on the throne, to the firstborn of the prisoner, who was in the dungeon, and the firstborn of all the livestock as well.”
The early monks used hour glasses and candles to mark the passing of the hours so that they could sing the liturgy of the hours. Lauds, 6:00 a.m.; Terce, 9:00 a.m.; Sext, noon; None -2:00 p.m.; Vespers, 6 p.m.; Compline 9 p.m.; and Invitatory - usually at 3:00 a.m. but also sung before the first prayer of the day. Bells rang for each. This system also measured the year since different psalms were sung throughout the year with I think the goal being that all the psalms would be read in a year’s time and the rest of the Bible in three years time.