The Divine Mercy Novena begins on Good Friday. The Directory on Popular Piety has this to say about the devotion:
"In connection with the octave of Easter, recent years have witnessed the development and diffusion of a special devotion to the Divine Mercy based on the writings of Sr. Faustina Kowalska who was canonized 30 April 2000. It concentrates on the mercy poured forth in Christ's death and resurrection, fount of the Holy Spirit who forgives sins and restores joy at having been redeemed. Since the liturgy of the Second Sunday of Easter or Divine Mercy Sunday - as it is now called- is the natural locus in which to express man's acceptance of the Redeemer's mercy, the faithful should be taught to understand this devotion in the light of the liturgical celebrations of these Easter days. Indeed, "the paschal Christ is the definitive incarnation of mercy, his living sign which is both historico-salvific and eschatological. At the same time, the Easter liturgy places the words of the psalm on our lips: "I shall sing forever of the Lord's mercy" (Ps 89 2)" DIRECTORY ON POPULAR PIETY AND THE LITURGY
"Jesus I trust in you!" is an absolutely wonderful prayer that can be prayed many, many times a day.