I just want to emphasize that the chaplet is extra-powerful when you say it while the person is dying, as Jesus said: "when they say this prayer in the presence of the dying, I will stand between my Father and the dying person, not as a just Judge but as a merciful Savior. " There is a sense of immediacy here when the person is in the throes of death, and when someone is praying for him. As Jesus said: “the grace of eternal salvation for certain souls in their final moment DEPENDS on your prayer.”
Yes, I have no doubt that salvation depends on prayer, and that it is good to pray when someone is dying. St. Faustina had a gift that she could tell if somebody was dying two buildings away or half a continent away.
Most of us are not St. Faustina. We may not hear that our loved one suddenly died in an accident until the day after it happened. I have had a friend die by drowning and since they could not find his body for a month we didn’t know for sure in the first few days if he was actually dead, and the family didn’t even release the info that he had jumped into a river for about 2 days after it happened because they were justifiably upset.
When my father died, he was dead before I heard about it. When my mother was dying, due to a lot of messed-up circumstances I was not there praying for her…and at that point I had never heard of the Divine Mercy chaplet. So even if I’d had it together to be there and praying for her, I could not have said the Divine Mercy.
Do you think Jesus would say to me, or anyone in one of the million circumstances above, that if we happened to pray this chaplet or any other prayer “late”, the prayer would not be “extra-powerful” for us, and the guy who happened to be at his loved one’s dying bedside got his loved one saved because the prayer was “extra-powerful” for him but my loved one got more severely judged or even went to Hell because for a whole variety of reasons, I didn’t pray it at the right moment?
Once again, this “extra-powerful” stuff is treating prayer like a magic charm, which is not the right outlook. Yes, it’s good to pray in the presence of the dying. Yes, it’s good to say the Divine Mercy prayer for someone who’s dying, or even someone who’s not dying or someone who’s already dead, but as the other person said, God can apply these prayers in the past if we need Him to, or apply them in the future if we need Him to. We’re not all St. Faustina who could tell when somebody was dying and pray for them right then, and God doesn’t expect that in order to make full use of our prayers.
P.S. We should also remember that the highest and greatest form of prayer to help any deceased soul is always to offer a Mass for them.