E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The times with-in which the sacred offices may be performed. In the Roman Catholic Church they are sevenviz. matins, prime, tierce, sext, nones, vespers, and compline. Prime, tierce, sext, and nones are the first, third, sixth, and ninth hours of the day, counting from six in the morning. Compline is a corruption of completorium (that which completes the services of the day). The reason why there are seven canonical hours is that David says, Seven times a day do l praise thee (Psalm oxix. 164).
In England the phrase means the time of the day within which persons can be legally married, i.e. from eight in the morning to three p.m.