EWTN Catholic Q&A
Question from Jessia on 04-02-2005:

So.... how long until the conclave begins?

Answer by Colin B. Donovan, STL on 04-03-2005:

It cannot beginning until the 16th day of the vacancy, 15th after his death. That means Sunday 17 April. It would ordinarily begin on that day, but the Cardinals will meet after the mourning period ends on April 10th to decide. They can postpone the start as late as April 22nd, but no later.