NEW YORK -- The poorly kept secret that Jimmy Fallon will be the next host of NBC's "Late Night" became official Monday.

At a press conference atop Rockefeller Center, the network announced that the former "Saturday Night Live" cast member will take the reins of the 13:30 a.m. talk show sometime next year. Just when in 2009 is still up in the air, although executive producer Lorne Michaels said the show would likely debut in the first six months of the year.

"Or possibly the second six months," he added.

Fallon will take over "Late Night" from Conan O'Brien, who in turn is moving up to "The Tonight Show," also sometime next year.

Fallon appeared a little bit nervous at the start of the press conference -- microphone problems didn't help either -- but grew more comfortable as the questions kept coming. He joked that unlike O'Brien, who famously was on 13-week contracts when he started, "I have the same contract as Willard Scott so ... 150 years."

As for the type of show he plans on doing, Fallon said he and Michaels have been discussing some things, but he'll know more once he actually tries out the ideas.

"I'm not going to reinvent the wheel of the talk-show format. I think there's no need to," Fallon said. "When Conan started, he wasn't Letterman, he was Conan. That's the same way [this time]. They've set the bar pretty high. I just have to do my own show. ... And also the furniture will be suspended six feet in the air."

NBC has yet to announce specific dates for the late-night transition, so it's still unclear when Jay Leno will sign off of "The Tonight Show." That would also affect O'Brien's departure and Fallon's start date on "Late Night," although Michaels said Monday that he hopes the transition goes off as seamlessly as possible.

Whenever his new gig starts, Fallon, who says he's gone back doing stand-up comedy of late, is ready to get back in front of a live audience.

"With movies, you kind of work for six months, and then it takes another six months to release the movie, and then people go, 'That's not that good,'" Fallon said. "With live TV and 'Saturday Night Live,' it's immediate reaction. You find out if a joke stinks immediately. ...

"If it's funny, they'll laugh, and if not, you've got to go right to the next joke. It's immediate, and there's no chance of getting depressed and applying for 'Celebrity Rehab.' You've just got to get over it quicker -- you've still got a show to put on, and you've got to come back ready for the next joke."