The Marian Antiphons are prayed following Night Prayer (Compline) in the Liturgy of the Hours (Divine Office). The Marian Antiphons, which honor the Blessed Virgin Mary, changed with the liturgical seasons. Different seasons traditionally employed different Marian Antiphons.
Here is the schedule for the four traditional Marian antiphons sung after Compline throughout the year.
1) From Ordinary Time to Advent, the change to the Alma Redemptoris Mater takes place after Evening Prayer I of Advent Sunday (that is, on Saturday night).
2) Ave Regina Caelorum begins after Evening Prayer I on February 1 if February 2 (the Feast of the Presentation) falls on a Sunday. If February 2 does not fall on a Sunday, we begin singing Ave Regina Caelorum on February 2, not the night before, and this song is is sung through Lent.
3) The switch to Regina Caeli (Queen of Heaven) begins at Evening Prayer II of Easter and ends with the resumption of Ordinary Time.
4) Salve Regina begins with Night Prayer after Evening Prayer II on Pentecost.
The use of the Marian Antiphons at the end of Compline, before retiring for the night, enables the faithful to commend themselves to their loving, heavenly mother whose tender love will be with them as they sleep. These are like one's earthly mother tucking her children into bed at night.