What's all this "book of hours' about?

This is a book of hours.
Basically, I'm making an online one that uses modern texts and modern prayers. Like, for the little office of the blessed virgin Mary, I used the office in the Liturgy of the Hours, except the translation is a compilation of my others work and some of my own. In total, I'll do the office of the Blessed Virgin, the office of the Holy Spirit, of the Holy Cross, of the Precious Blood, of the Holy Trinity, and of Ss.Peter and Paul.
I'll add the seven penitential psalms and the litany of the saints, the office of the dead, and suffrages to Ss.Peter and Paul, S. John Neumann, S. Thomas Beckett, S. Micheal, and the 14 Holy Helpers.
Some prayers before and after communion, the litany of the blessed virgin, of the Sacred Heart, of the Precious blood, of the Holy Name, of S.Joseph, and some less known ones. Lastly, a guide to attending mass devoutly and reverently by S. Francis de Sales.