That is something that Catholic traditions do and encourage. There is some thought that eternity is somewhat outside of what we perceive as time. When a Catholic has communion, they have it with Christ and the Church of believers. Note - *All* believers. Not just those in the room, or those in the country, but also those in the past, those in the present, and even (I suppose) those in the future. Communion is, in a sense, with something that is outside of time.
In the same way, a prayer could also be outside of time, and beneficial in a sense, retroactively? At least that is what my interpretation is. I would also note, that in the previous posts it was said that God is the judge. Specifically, I would say from verses in the Gospel of John, Christ says that the Father has committed all judgement to me.
I was once talking with a man who was a sniper in the middle east. Because his targets were not Christian, he said 'I sent those people to hell'. 'No,' I said. 'You didn't send them to Hell. You sent them to Christ. Christ will decide if he likes the look of them or not.'
Just my 2 cents.