The Mets had been pointing to May 1 as an estimated return date for Parnell, who had Tommy John surgery last April. The righthander will begin the season on the disabled list.
Parnell faced opposing hitters for the first time since the surgery on Wednesday, when he threw 17 pitches against the Marlins' Triple-A team. He is expected to throw a minor league side session Sunday.
"Make sure you get your tickets," Parnell told ESPN's Adam Rubin.