Why should you pray three times a day? Because David, Daniel, and Peter prayed three times a day. They set a model for us to follow.
David said, “Evening and morning and at noon I will pray, and cry aloud, And He shall hear my voice” (Psalm 55:17 NKJV). Here it specifically says David prayer three times a day
The Prophet Daniel also got down on his knees three times a day and prayed and gave thanks before his God, as he had done previously (Daniel 6:10). This was a habit of the devout.
In Acts 2:15, it says that Peter prayed with the church at “nine o’clock in the morning.” In Acts 3:1, “One day Peter and John were going up to the temple at the hour of prayer, at three o’clock in the afternoon.” And in Acts 10:9, Peter went up to the housetop to pray at “about noon.”
This practice was passed down to the early Church. The Didache, the earliest document after the New Testament about Church practice. It says to pray the Lord’s Prayer “three times a day” (Didache 8:2-3).
Here we see a set prayer was repeated three times a day. Hence, the foundation for the liturgy of the hours, also known as the Divine Office.