Divine Mercy Novena

The nine days Faustina was asked to pray, each one for a different group of souls.

Length.
9 days.
Traditionally prayed.
Good Friday to Divine Mercy Sunday
Sources.
Built from public-domain prayers plus original daily meditations written for this site.

If you miss a day, pick up where you left off. Nine consecutive days is the tradition and it is worth keeping when you can, but a broken chain does not undo what you have prayed, and starting again from day one is your choice rather than a penalty.

About the saint this novena asks