breviary -

"In liturgical language Breviary has a special meaning, indicating a book furnishing the regulations for the celebration of Mass...  It is divided into four parts according to the seasons of the year: Winter, Spring, Summer, and Autumn."  It contains psalms, offices for all seasons, gospels, a complete ecclestical calendar of events.  

"The prayer of the Breviary is meant to be used daily [my underlining]; each day has its own Office;  in fact it would be correct to say that each hour of the day has its own office, for, liturgically, the day is divided into hours founded on the ancient Roman divisions of the day, of three hours apiece -- Prime, Terce, Sext, None, and Vespers, and the night Vigils. In conformity with this arrangement, the Office is portioned out into the prayers of the night vigils, that is to say Matins and Lauds. Matins itself is subdivided into three nocturns, to correspond with the three watches of the night: nine o'clock at night, midnight, and three o'clock in the morning. The office of Lauds was supposed to be recited at dawn. The day offices corresponded more or less to the following hours: Prime to 6 A.M., Terce to 9 A.M., Sext to midday, None to 3 P.M., Vespers to 6 P.M. It is necessary to note the words more or less, for these hours were regulated by the solar system, and therefore the length of the periods varied with the season.  The office of Compline, which falls somewhat outside  the above division, and whose origin dates later than the general arrangement, was recited at nightfall." [The Catholic Encyclopedia]