Not set yet, but John Allen of the "N""C""R" has some good information on the General Congregation of Cardonals, which begins Monday. Soon afterwards we will know the Conclave start date, and Allen gives some reasoned guidelines:
We now know that the first meeting of the General Congregation, which brings together all the cardinals during the run-up to the conclave, is set for 9:30 a.m. Monday in Rome. In a break with practice from the last time around, the cardinals will also go back into the General Congregation on Monday afternoon.
As a reminder, all the cardinals are eligible to participate in the General Congregation meetings, not just the 115 under 80 who will actually cast ballots in the conclave. At the moment, there are a total of 207 cardinals, after the death Thursday of French Cardinal Jean Marcel Honoré at 92. Not all 207, however, will participate in the General Congregations; we'll know Monday how many actually showed up.
The first order of business is to establish the start date for the conclave, and the fact they're going back to work in the afternoon suggests there's a desire to try to get that nailed down as quickly as possible. (It's not yet clear whether the cardinals will continue going back in the afternoons for the rest of week.)
Given that some cardinals are still arriving, we'll have to wait until Monday to see if a consensus emerges quickly, or if they'll need more time to reach agreement.
For now, however, the most common view in Rome is that the cardinals will be anxious to move things along. For one thing, they've known this moment was coming since Feb. 11; for another, most of them want to be comfortably back in their dioceses by Holy Week, with Palm Sunday this year falling on March 24.
Most cardinals will stick around for the installation Mass of the new pope, which usually comes a few days after the conclave ends. (In 2005, Benedict XVI was elected on April 19 and his inaugural Mass was April 24). Working backward, and allowing for a conclave that's slightly longer than the day and a half it took last time, they would probably need to begin by March 11 at the latest to be sure of bringing the plane in for an on-time landing.
The most common theory in Rome holds that they may bring the curtain up even earlier, possibly as soon as the end of next week.
The Vatican Press Office has said it will hold briefings each day at 1 p.m. Rome time, meaning 7 a.m. on the East Coast, which on Monday might be the first window of opportunity for the announcement of an official date.