There is a long tradition, rooted in sacred scripture, behind the Liturgy of the Hours. Here are some links to sites with interesting, if obscure, facts about the history and practice.
US Conference of Catholic Bishops: Liturgy of the Hours
Divineoffice.org: How to Pray the Liturgy of the Hours
Universalis: Structure of Liturgy of the Hours
Liturgies.net: Invitatory Psalms
We encounter some differences over time in language, terminology, practice, and schedules for the Liturgy of the Hours. The chart below illustrates some of the variances. It is interesting to see how the community of Monks at Mepkin Abbey follow the practice of the ancients. Note the verse from Psalm 119 which may be the basis for the ancient schedule.