It still must happen within 20 days of his resignation, the pope said.
After his retirement, Benedict is expected to head to the pope's summer residence in Rome before eventually settling in a monastery in Vatican City. Church officials have said he will seek no influence over the election of his successor, or over management of the church.
Among other issues, Vatican officials are still trying to work out what Benedict will be called in retirement. One suggestion is "pontifex maximus," Celata said. The term can be translated as "supreme bishop."
Vatican officials hope to have an answer next week, Lombardi said.