I agree with Captain Poplar as to why Rocard couldn't be a candidate in 1995. I think, however, that his performance as Prime Minister (1988-1991), is essential to his credibility, so I would put the POD in 1993-1994.
2 possilibities: Rocard has an accident (boating, glider, or just a car accident) and cannot lead the Socialists for the European Elections of 94, but recovers swiftly enough to run for President in 1995
Bernard Tapie is unable to lead the Radical list (let HIM have an accident!) that did so much damage to Rocard's list. Without Tapie, the Radicals get their usual 4-5% of the vote and Rocard remains First Secretary of the Socialist Party and has a slim chance to beat Chirac in 1995
The other possibility for a POD would be Mitterrand not running in 1988, and it could only be because of his health. Lets not forget that he was diagnosed with cancer in 1981, and was not expected to live more than a couple of years. His recovery in OTL is actually quite miraculous.
With Mitterrand out of the picture in 1988, Rocard almost automatically gets the candidacy for the Socialist Party, and against Chirac, he has a pretty good chance to win.