189. Since it is a significant moment, a feast day is frequently preceded by a preparatory triduum, septinaria or novena. The “times and modes of popular piety”, however, should always correspond to the “times and modes of the Liturgy”.
These preparation periods are considered to have spiritual and catechetical value:
Tridua, septinaria, and novenas can be useful not only for honoring the Blessed Virgin Mary through pious exercises, but also to afford the faithful an adequate vision of the positions she occupies in the mystery of Christ and of the Church, as well as the the role she plays in it.
These periods, as well as the Marian observances that conclude them are intended to lead believers to Christ and the sacramental life of the Church:
Pious exercises cannot remain indifferent to the results of biblical and theological research on the Mother of Our Savior. These should become a catechetical means diffusing such information, without however altering their essential nature.
Tridua, septinaria and novenas are truly preparations for the celebration of the various feast days of Our Lady, especially when they encourage the faithful to approach the Sacraments of Penance and Holy Eucharist, and to renew their Christian commitment following the example of Mary, the first and most perfect disciple of Christ.
Not exactly a period of preparation, the 13th day of the month is sort of like a Saturday. I wonder if these are observed as Saturdays anywhere, with Mass and the Hours dedicated to the Virgin:
In some countries, the faithful gather for prayer on the 13th. of each month, in honor of the apparitions of Our Lady at Fatima.
The Directory on Popular Piety and the Liturgy is online at the Vatican site.