According to Media Matters (which doesn't provide a timeline, and neither does Napolitano):
On the October 31 broadcast of the nationally syndicated radio show The Radio Factor with Bill O'Reilly, guest host Andrew P. Napolitano -- who serves as Fox News' senior judicial analyst -- cited "at least one" of his Fox News colleagues who Napolitano said claimed to have been present at a party where former ambassador Joseph C. Wilson IV introduced Valerie Plame as "my CIA operative wife." Napolitano used this anonymous claim to question whether Plame "was, in fact, undercover" when her identity as a CIA employee was allegedly leaked to syndicated columnist Robert D. Novak, who published it in a July 14, 2003 column. I. Lewis "Scooter" Libby, Vice President Dick Cheney's former chief of staff, was indicted on October 28 for obstruction of justice, perjury, and false statements in connection with the leak investigation.
Napolitano did not explain why his mystery Fox News source has not publicly reported the story. Nor did he explain the apparent discrepancy between this claim and the Libby indictment, which states: "At all relevant times from January 1, 2002 through July 2003, Valerie [Plame] Wilson was employed by the CIA, and her employment status was classified. Prior to July 14, 2003, Valerie Wilson's affiliation with the CIA was not common knowledge outside the intelligence community."
So I guess Mr. Napolitano will be expecting to hear from Patrick Fitzgerald.