In His revelations to St. Faustina, Our Lord asked for a special prayer and meditation on His Passion each afternoon at the three o’clock hour, the hour that recalls His death on the cross.
At three o’clock, implore My mercy, especially for sinners; and, if only for a brief moment, immerse yourself in My Passion, particularly in My abandonment at the moment of agony. This is the hour of great mercy. In this hour, I will refuse nothing to the soul that makes a request of Me in virtue of My Passion (Diary, 1320).
As often as you hear the clock strike the third hour, immerse yourself completely in My mercy, adoring and glorifying it; invoke its omnipotence for the whole world, and particularly for poor sinners; for at that moment mercy was opened wide for every soul. In this hour you can obtain everything for yourself and for others for the asking; it was the hour of grace for the whole world — mercy triumphed over justice. (1572)
My daughter, try your best to make the Stations of the Cross in this hour, provided that your duties permit it; and if you are not able to make the Stations of the Cross, then at least step into the chapel for a moment and adore, in the Most Blessed Sacrament, My Heart, which is full of mercy; and should you be unable to step into the chapel, immerse yourself in prayer there where you happen to be, if only for a very brief instant. (1572)
From these detailed instructions, it’s clear that Our Lord wants us to turn our attention to His Passion at the three o’clock hour to whatever degree our duties allow, and He wants us to ask for His mercy.