42 This constant union with God is best achieved and preserved through the various practices of priestly piety; many of the more important of them, such as daily meditation, visits to the Blessed Sacrament, recitation of the Rosary, careful examination of conscience, the Church, in her wise and provident regulations, has made obligatory for priests. (54) As for the hours of the Office, priests have undertaken a serious obligation to the Church to recite them. (55)
Source: Sacerdotii Nostri Primordia (Vatican.va)