In Pope John Paul II’s norms, Universi Dominici Gregis, it was established that among the tasks given to the General Congregations of Cardinals (composed of both electors and non-electors) during a Vacancy was the authority to decide whether to begin the Conclave on the 15th day after the Vacancy, or for sufficient reason to postpone it to as late as the 20th day. The delay between the Vacancy and the Conclave allowed both for days of mourning and the travel of the Cardinals to Rome.
The resignation of the Pope, however, not only provides pre-notice of a Vacancy but also one which does not require a funeral or mourning period. Pope Benedict’s changes, therefore, grant to the Cardinals the faculty (or grant of authority) to decide whether to begin earlier than the 15th day, provided “all the Cardinal electors are present” (NN 37). They may not decide to begin later than the 20th.