ChapterII-V. Daytime Hours
74. Following a very ancient tradition Christians have made a practice of praying out of private devotion at various times of the day, even in the course of their work, in imitation of the Church in apostolic times. In different ways with the passage of time this tradition has taken the form of a liturgical celebration.
75. Liturgical custom in both East and West has retained midmorning, midday, and midafternoon prayer, mainly because these hours were linked to a commemoration of the events of the Lord's passion and of the first preaching of the Gospel.
76. Vatican Council II decreed that these lesser hours are to be retained in choir. 
The liturgical practice of saying these three hours is to be retained, without prejudice to particular law, by those who live the contemplative life. It is recommended also for all, especially those who take part in retreats or pastoral meetings.
77. Outside choir, without prejudice to particular law, it is permitted to choose from the three hours the one most appropriate to the time of day, so that the tradition of prayer in the course of the day's work may be maintained.
78. Daytime prayer is so arranged as to take into account both those who recite only one hour and those who are obliged, or desire, to say all three hours.
79. The daytime hours begin with the introductory verse, God come to my assistance with the Glory to the Father, As it was in the beginning, and the Alleluia (omitted in Lent).
Then a hymn appropriate to the hour is sung. The psalmody is next, then the reading, followed by the verse. The hour concludes with the prayer and, at least in recitation in common, with the acclamation, Let us praise the Lord. R. And give him thanks.
80. Different hymns and prayers are given for each of the hours so that, in keeping with tradition, they may correspond to the true time of day and thus sanctify it in a more pointed way. Those who recite only one hour should therefore choose the texts that correspond to the true time of day.
In addition, the readings and prayers vary in keeping with the character of the day, the season, or the feast.
81. Two psalmodies are provided: the current psalmody and the complementary psalmody. Those who pray one hour should use the current psalmody. Those who pray more than one hour should use the current psalmody at one hour and the complementary psalmody at the others.
82. The current psalmody consists of three psalms (or parts in the case of longer psalms) from the psalter, with their antiphons, unless directions are given to the contrary.
On solemnities, the Easter triduum, and days within the octave of Easter, proper antiphons are said with three psalms chosen from the complementary psalmody, unless special psalms are to be used or the celebration falls on a Sunday, when the psalms are those from the Sunday of Week I of the psalter.
83. The complementary psalter consists of three sets of three psalms, chosen as a rule from the Gradual Psalms.