The Vatican has announced that there is indeed a possibility that the Conclave may begin earlier than the earlier announced 15-20 March 2013 timeframe. This is because unlike normal period of sede vacante (or vacant See ‘of Rome’) due to the death of the previous Pope, Pope Benedict XVI’s decision to retire and renounce the Papacy has been announced well ahead of the actual date of beginning of the sede vacante.
Thus, the Cardinals have ample time to prepare for the Conclave and travel to Rome by the time the See becomes vacant on 28 February 2013 at 8.00 pm Rome time. This would then allow the Conclave to begin much earlier, perhaps in early March 2013, and will allow a new Pope to be elected immediately, and then the new Pope can already be installed (at St. Peter’s Square ceremony of the imposition of the pallium and the Fisherman’s Ring) and enthroned (at the Basilica of St. John Lateran, the Cathedral of Rome), before the Holy Week begins on Palm Sunday (24 March 2013).
If the Conclave begins only on the 15th of March or even later, there would be no time left available for the Pope to be properly installed and enthroned before the busy Holy Week begins. Another advantage is also that the Cardinal-electors (especially the residential Archbishops and bishops of Archdioceses and dioceses around the world) can return to their home and celebrate the Holy Week with their diocese/archdiocese, rather than be stuck in Rome due to the late Conclave.