98 Members of any institute dedicated to acquiring perfection who, according to their constitutions, are to recite any parts of the divine office are thereby performing the public prayer of the Church. They too perform the public prayer of the Church who, in virtue of their constitutions, recite any short office, provided this is drawn up after the pattern of the divine office and is duly approved.
Source: Sacrosanctum Concilium (Vatican.va)