He has spent more time preparing in his cavernous studio with his staff than in his expansive new home in tony Brentwood with his wife, Liza, and two kids, Neve, 5, and Beckett, 3.
"'The Tonight Show' means everything to me," O'Brien says, noting he used to watch Carson with his father. "I'll have good moments and bad, but I'll keep coming at it."
O'Brien "has the summer to establish himself," says Bill Carter, author of "The Late Shift: Letterman, Leno and the Network Battle for the Night," which chronicled the jockeying for Carson's throne that led to tension between Leno and Letterman.
Carter adds that O'Brien should not expect to match Leno's ratings, "but Conan has a loyal, younger core audience that he can work on expanding."
Few expect the general appeal of either NBC star to change. Leno, who consistently won the ratings battle against Letterman's "Late Show" on CBS, is known for attracting an older audience than O'Brien.
Leno also routinely pulled larger audiences, averaging just more than 5 million viewers a night this season compared with O'Brien's 1.9 million in the following hour, according to Nielsen.
"These shows are consistent and their content is safe, if not particularly buzzworthy," says Sam Armando, director of audience analysis for Starcom Worldwide, a Chicago-based media agency. "You're not going to get a huge bump (in viewership) the way you would with a hit scripted show or an 'American Idol,' but the flip side is that you know exactly who's watching."
Armando says O'Brien isn't likely to change his style much.
"He's been popular for many years doing what he does, so it wouldn't make sense for NBC to ask him to switch things up," he says. "They'll welcome a slightly younger audience to The Tonight Show that will keep growing up with Conan. Then there's (Jimmy) Fallon (who took over O'Brien's "Late Night") helping bring in the new young crowd. And the best part is, NBC doesn't have to worry about competing with Jay on another channel."
O'Brien isn't worrying specifically about Leno. He's worrying about everything.
"At 4 a.m., I do wake up sometimes and go, 'Oh my God, it's The Tonight Show,' " he says, draped across a chair in his office, a few feet away from a Martin acoustic and a Gretsch electric guitar that help him unwind. "But nothing funny comes out of reverence. I'll take care of this franchise. The key is to put aside the fear and say, 'Let's just make some people laugh.' "
That comes easily for O'Brien, who during an hour-long conversation riffs on L.A. car culture ("I'd like to walk to work like I did in New York, but we'd do like one show a week"), his passion for the Military Channel ("My wife always wants to unwind and watch comedies, but I need to see how forensic scientists have found new clues to the Battle of the Bulge") and the future of TV.
"The show I do on June 1 is likely to be totally different from the one we do six months later," he says. In today's fragmented viewing world, "everything's changing. It's crazy. That's why I'm just going to stick with what makes me smile."
How long does he envision hosting this show?
"Until I'm 160, because there will be medical advancements," he says. "Fallon will take over for me when I retire at 108 to travel with my family. But it won't be Jimmy, it'll be his brain in a jar."
Memories of Carson