Mark 15:25, 33 And it was the third hour, and they crucified Him... And when the sixth hour was come, there was darkness over the whole earth until the ninth hour.
Because Jesus was on the Cross between the hours of Noon and 3:00 PM, these three hours today are considered the most sacred of all. A devotion called "Tre Ore" or "Three Hours' Agony" might be held at this time; if not, you can do it yourself by meditating on His Passion -- reading the Gospel narratives of the Passion, making the Stations of the Cross by yourself, praying the Sorrowful Mysteries of the Rosary, praying the Litany of the Passion, etc. Draw the curtains, take the phone off the hook, turn off televisions and radios, quiet your environment and yourself, and meditate on what Christ has done for you. At 3:00, "The Hour" He died, the atmosphere should be as if you are standing next to the deathbed of your father who died a moment ago.
O My people, what have I done to thee? Or wherein have I afflicted thee? Answer Me. Because I led thee out of the land of Egypt, thou hast prepared a Cross for thy Savior.
A second choir responds to each of those Reproaches with a trisagion in Greek and Latin. You might recognize its English translation if you've ever prayed the Divine Mercy chaplet:
O holy God! O holy God! O holy strong One! O holy strong One! O holy immortal One, have mercy on us. O holy immortal One, have mercy on us!
The remaining nine Reproaches are answered with the response " O my people, what have I done to thee? or wherein have I afflicted thee? Answer me." ("Popule meus, quid feci tibi? aut in quo constristavi te? responde mihi."). The words evoke awe in reminding us of our ancient Israelite heritage -- and evoke humility in recalling how our ancestors failed repeatedly:
For thy sake I scourged Egypt with its first-born: and thou didst deliver Me up to be scourged.
After the Reproaches, we receive Communion, receiving Hosts consecrated at yesterday's Mass.