The Chaplet can be said anytime but the Lord specifically asked that it be recited as a novena especially on the nine days before the Feast of Mercy (starting on Good Friday). And He promised, "By this Novena (of Chaplets), I will grant every possible grace to souls" (796).
Encourage souls to say the Chaplet which I have given you (1541). Whoever will recite it will receive great mercy at the hour of death (687). When they say this Chaplet in the presence of the dying, I will stand between My Father and the dying person, not as the just Judge but as the Merciful Savior (1541). Priests will recommend it to sinners as their last hope of salvation. Even if there were a sinner most hardened, if he were to recite this Chaplet only once, he would receive grace from My infinite mercy (687). I desire to grant unimaginable graces to those souls who trust in My mercy (687). Through the Chaplet you will obtain everything, if what you ask for is compatible with My will. (1731)
In addition to the Novena to The Divine Mercy, which our Lord gave to Saint Faustina for her own personal use, He revealed to her a powerful prayer that He wanted everyone to say called the Chaplet of Divine Mercy. Saint Faustina prayed the Chaplet almost constantly, especially for the dying, and the Lord urged her to encourage others to say it, too, promising extraordinary graces to those who would recite this special prayer.
We can pray this Novena of Chaplets for our own personal intentions or we can offer it together with the Novena to The Divine Mercy for the daily intentions dictated by our Lord to Saint Faustina.
First Day - all mankind, especially all sinners
Second Day - the souls of priests and religious
Third Day - all devout and faithful souls
Fourth Day - those who do not believe in God* and those who do not yet know Me
Fifth Day - the souls of those who have separated themselves from My Church
Sixth Day - the meek and humble souls and the souls of little children
Seventh Day - the souls who especially venerate and glorify My Mercy
Eighth Day - the souls who are detailed in purgatory
Ninth Day - souls who have become lukewarm