How the saying of the Hours first began, and why they are so called
The first that now we find in scripture to have used the worshipping of God at certain hours of the day, was Daniel the prophet, as it appeareth in his sixth chapter. And in the New Testament, in the Acts of the Apostles, the tenth chapter, we read that S. Peter the Apostle accustomed himself to certain hours of prayer. By which examples (as S. Cyprian testified) the Catholic Church of Christ did first receive and admit such manner of praying.
Whereupon the same usual service that we call Pryme and Hours, was first instituted to be said and sung in the churches of England, according to the custom and use of the Diocese; somewhere after Use of Sarum, and somewhere after the Use of York. And therefore when we read Hora Prima, Tertia, Sexta, Nona, that is the first, the third, the sixth and the ninth hour, even as they make mention of several hours, so were they; and they may be used at several times of the day, to be said in remembrance of Christ’s passion, and the compassion of the Virgin Mother.
The Psalter, or Seven ordinary Hours of Prayer ~ transl. & edited by John David Chambers, p. 5.