Staffan de Mistura told the pan-Arab newspaper Al-Hayat it was his "intention" for the talks aimed at ending Syria's five-year war to begin in the afternoon of March 9.
But he said he expected them to begin in earnest on the following day.
"I think that we will begin on March 10. That is when the process will start," he said according to an Arabic translation of his remarks published by the newspaper.
He said preparatory meetings will be held ahead of "in-depth discussions separately" which each faction.
A first round of talks in early February was cut short amid intensifying Russian air strikes in Syria in support of President Bashar al-Assad's forces.
But a fragile ceasefire drawn up by Russia and the United States and backed by the UN Security Council that entered into force on February 27 is now in its second week, despite accusations of violations.