Here is a prayer for 3 o'clock, but you don't necessarily have to say this one. The important thing is to say something - to honor Our Lord's sacrifice, who chose to save us from a fate we deserve, and to approach the Fount of mercy, which was opened up "for the washing of the sinner, and of the unclean woman" (Zechariah 13:1). Our Lord died for us; He died for a reason not to be put on our wall or in a textbook but to be placed in our hearts to make us remember we are to be Eucharistic tabernacles to let the light of Christ to shine through us. We can never forget the Lord's infinite love.
The Prayer:
O Divine Jesus, we transport ourselves in spirit to Mount Calvary to ask pardon for our sins which are the cause of Thy death. We thank Thee for having thought of us in that solemn moment, and for having made us children of Thy own Mother.
Holy Virgin, show thyself our Mother by taking us under thy special protection.
S. John, be our patron and model, and obtain for is the grace of imitating thy filial piety of Mary, our Mother. Amen.
Source: Christian Warfare