While a detailed explanation of the Liturgy of the Hours (also known as the “Divine Office” and the “Divine Hours”) is forthcoming, I should mention that the year is divided unto four volumes: Volume I deals with the Advent and Christmas seasons; Volume II deals with the Lenten and Easter seasons; Volume III deals with the weeks in Ordinary Time (that is, outside of any season) between the Christmas and Lenten seasons; Volume IV deals with the weeks in Ordinary Time between the Easter and Advent seasons. It seems we just began Volume III.
There have been many changes to the Liturgy of the Hours since Vatican II, but most of these changes have been good: they have simplified the practice, making it more appealing to the laity to join in these prayers. Rather than simply being the Church’s prayer in the mouth of clergy and religious, it is now the Church’s prayer in the mouth of all types of members thereof.
Before Vatican II, though, the last major reform was during the pontificate of Pope St. Pius X. As his pontificate was not too long ago and as his changes were quite sweeping, one cannot claim that Vatican II’s changes did away with anything ageless. (If I remember correctly, the popes after him, to give some perspective, have been Blessed John XXIII, Paul VI, John Paul I, John Paul II, and Benedict XVI.)
(For Tuesday, February 21, AD 2007, Ash Wednesday, the first day in the season of Lent, the first penitential day of Lent.)