Traditionally the Novena to the Immaculate Conception is prayed nine days prior to December 8th so that it ends on the feast day. But since any novena can be prayed at any time.
"[How to prepare for the feast of the Immaculate Conception] . . . But how can we honor Mary these days so as to merit Her protection? I shall not insist on frequent reception of the sacraments. You already know that Don Bosco has nothing more at heart than this. But I will suggest two particular things to each of you in Mary’s honor.
First, put your whole heart into this novena; second, prepare a bouquet of flowers for Her feast day. How? By picking a flower each day. But where, when no flowers are blooming in this cold winter? From the garden of your hearts. What sort of flowers? Some little act of virtue to be practiced each day in honor of Mary Immaculate.
Let each one take this to heart, so that on the dawn of this great feast there will be as many bouquets as boys, and each bouquet will have a flower for every day of this novena. You may be sure that Our Lady will be quite pleased with your gift."