88 Because the purpose of the office is to sanctify the day, the traditional sequence of the hours is to be restored so that once again they may be genuinely related to the time of the day when they are prayed, as far as this may be possible. Moreover, it will be necessary to take into account the modern conditions in which daily life has to be lived, especially by those who are called to labor in apostolic works.
Source: Sacrosanctum Concilium (Vatican.va)