But since the Church is now dealing with an announced resignation and not a sudden death, Vatican spokesman Federico Lombardi said the Vatican would be "interpreting" the law to see if it could start earlier.
Cardinals around the world have already begun informal consultations by phone and email to construct a profile of the man they think would be best suited to lead the Church in a period of continuing crisis.
The Vatican appears to be aiming to have a new pope elected and then formally installed in a solemn ceremony before Palm Sunday on March 24 so he can preside at Holy Week services leading to Easter.
The 85-year-old Benedict was having as normal a Saturday as possible, considering that his remaining scheduled public appearances can now be counted on one hand.
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The Vatican has been at pains to stress that the pope was leaving exclusively because of diminishing spiritual and physical forces and that the pontiff was certain it was the right thing to do and would not hurt the Church.
"Benedict is not abandoning us in times of difficulty," Lombardi said in his weekly editorial for Vatican Radio. "With confidence, he is inviting the Church to trust in the Spirit and in a new successor of St. Peter."
Benedict's papacy was rocked by crises over sex abuse of children by priests in Europe and the U.S., most of which preceded his time in office but came to light during it.
His reign also saw Muslim anger after he compared Islam to violence. Jews were upset over his rehabilitation of a Holocaust denier. During a scandal over the Church's business dealings, his butler was convicted of leaking his private papers.
Meanwhile, new details emerged on Saturday about the state of Benedict's health in the months before his shock decision.
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Peter Seewald, a German journalist who wrote a book with the pope in 2010 in which Benedict first floated the possibility of resigning, visited him again about 10 weeks ago and asked what else could be expected from his papacy.
According to excepts published in the German magazine Focus, the pope answered: "From me? Not much from me. I'm an old man and the strength is ebbing. I think what I've done is enough."
Asked if he was considering resigning, the pope said: "That depends on how much my physical strength will force me to that."
Seewald said he was alarmed about the pope's health.
"His hearing had deteriorated. He couldn't see with his left eye. His body had become so thin that the tailors had difficulty in keeping up with newly fitted clothes. ... I'd never seen him so exhausted-looking, so worn down."
Keeping to his schedule, Benedict met a group of Italian bishops and Guatemala's president on Saturday morning and in the afternoon was receiving caretaker Italian Prime Minister Mario Monti in a farewell audience.
Monti, a devout Catholic, is leading a centrist coalition in next week's elections but the Vatican says the farewell meeting has nothing to do with the vote.
On Sunday, the pope will hold his customary noon blessing from his window overlooking St Peter's Square before going into a previously scheduled, week-long Lenten spiritual retreat. He will emerge from that on Feb. 23.
He will then say one more Sunday noon prayer on Feb. 24, hold a final general audience on Feb. 27. The next day he will take a helicopter to the papal summer retreat at Castel Gandolfo, south of Rome, flying into the history books.
Vatican officials said he would stay there for the two months or so needed to restore the convent inside the Vatican where he will live out his remaining years.