We still don’t know as of today when the conclave will start, although it appears that the cardinals will not even gather to discuss it until Monday, March 4.
By now, most of the cardinal-electors are in Rome or will soon be there.
Currently, the rules say that the cardinals must wait for 15 full days after the throne of Saint Peter becomes “sede vacante” before a conclave can start. This allows time for the funeral services of the deceased pope and for all the cardinals to get to Rome.
In recognition of the unique circumstances brought on by his resignation, Pope Benedict XVI issued an apostolic letter “motu proprio” (on his own initiative) on Feb. 25 changing the rules, letting the cardinals move the date up if all of them are present. Even so, the conclave must begin no more than 20 days (March 20) after the start of sede vacante.
There has been a lot of chatter about cardinals hoping to have a new pope inaugurated before the beginning of Holy Week, which kicks off with Palm Sunday on March 24. Easter Sunday is March 31.
So there are your key dates: The conclave will not begin before March 4 or after March 20.