Christ connected the Divine Mercy to His Second Coming in His revelations to Sister Faustina. His First Coming was in humility to redeem the world, but His Second Coming will be in glory to judge the world.
Some private revelations Christ has given to Sister Faustina.
You will prepare the world for My final coming. (Diary 429)
Speak to the world about My mercy . . . It is a sign for the end times. After it will come the Day of Justice. While there is still time, let them have recourse to the fountain of My mercy. (Diary 848)
Tell souls about this great mercy of Mine, because the awful day, the day of My justice, is near. (Diary 965)
I am prolonging the time of mercy for the sake of sinners. But woe to them if they do not recognize this time of My visitation. (Diary 1160)
Before the Day of Justice, I am sending the Day of Mercy. (Diary 1588)
He who refuses to pass through the door of My mercy must pass through the door of My justice. (Diary 1146)
The Blessed Virgin, the Mother of Mercy, gave to Sister Faustina a revelation about Christ.
You have to speak to the world about His great mercy and prepare the world for the Second Coming of Him who will come, not as a merciful Savior, but as a just Judge. Oh how terrible is that day! Determined is the day of justice, the day of divine wrath. The angels tremble before it. Speak to souls about this great mercy while it is still the time for granting mercy. (Diary 635)
Only the Almighty Father knows the exact timing of Christ Second Coming.