Through the praying of the Liturgy of the Hours, the Church sanctifies the entire day in praise of Almighty God.
Put another way, the Divine Office is a kind of 'extension' of Holy Mass.
The Liturgy of the Hours is also known as the "Divine Office" or "The Breviary,"
The mystery of Christ, his Incarnation and Passover, which we celebrate
in the Eucharist especially at the Sunday assembly, permeates and
transfigures the time of each day, through the celebration of the
Liturgy of the Hours, "the divine office." This celebration, faithful to
the apostolic exhortations to "pray constantly," is "so devised that
the whole course of the day and night is made holy by the praise of
God."
Catechism of the Catholic Church #1174
The liturgy of the Hours is an Official Liturgy of the Church, with its own ceremonies and rites
Vatican II
"Pastors of souls should see to it that the chief hours [i.e. Lauds and Vespers],
especially Vespers, are celebrated in common in church on Sundays and
the more solemn feasts. And the laity, too, are encouraged to recite the
divine office, either with the priests, or among themselves, or even
individually."
Sacrosanctum Concilium #100 Constitution On the Sacred Liturgy December 4, 1963