‘Late Show With Stephen Colbert’ will premiere Sept. 8, CBS says

CBS has scheduled Stephen Colbert’s new late-night show to start Sept. 8. And that means the clock is ticking for the former host of “The Colbert Report” to crack the code of one of network TV’s most storied -- and now most competitive -- formats.

First up: Deciding whether he wants to do an opening monologue, a time-honored tradition that dates back to NBC’s “Tonight Starring Steve Allen” in the mid-1950s.

“He’s working on that now,” Nina Tassler, chairman of CBS Entertainment, told reporters Monday morning at the TV press tour in Pasadena, where she revealed the specific launch date of “Late Show With Stephen Colbert” and provided other details.

With David Letterman set to retire later this year after more than 30 years in late-night TV -- more than 20 of them on CBS -- the network is in the midst of a major transition. And questions about Colbert and James Corden -- whose own show replaces Craig Ferguson’s 12:35 a.m. program starting in March (CBS is using guest hosts in the meantime) -- dominated Tassler’s session Monday.

That Colbert and his producers are even keeping their options open with the monologue suggests how far they might go with a reinvention. It also underscores how much leeway he is being given by his new bosses.

CBS is “letting him do what he wants to do,” Tassler said.

The network has already said that Colbert will be shedding his persona from “The Colbert Report,” that of a self-absorbed, overbearing right-wing pundit. Tassler promised on Monday that viewers would get to know “the real Stephen Colbert.”

One difference that might set Colbert’s new show apart from NBC’s “Tonight Show Starring Jimmy Fallon” or ABC’s “Jimmy Kimmel Live” -- a continuing focus on politics.

Tassler promised a show “still topical, still relevant, still dealing with current events.”

There will be music and guests, she added, but they may be incorporated into the mix in unusual ways. “There will be parts that will be traditional in some contexts and there will be things he wants to do differently,” Tassler said. “He’s a real student of media. He knows the format better than anybody.”

Meanwhile, CBS is turning its sights to Corden, a 36-year-old British actor and TV host all but unknown in the U.S. when the network picked him last year as Ferguson’s successor.

Tassler said that she and her boss, CBS chief Leslie Moonves, met with Corden in New York when interviewing candidates for the job.

“To say that we were mesmerized is an understatement,” she said. “He’s a combination of Jack Black and Fred Astaire.”

As for CBS’ prime-time lineup, Tassler announced that the network had ordered second seasons of three freshman dramas: “Madam Secretary,” “NCIS: New Orleans” and “Scorpion.” However, the network had no good news for another new drama, the ratings-challenged crime thriller “Stalker,” although Tassler left open the possibility that it might yet be reordered.

Tassler also took note of broad shifts changing the TV landscape, including increased reliance on video-on-demand and DVR playback. Networks fretting over ratings dips are aggressively pushing the idea of reporting viewing that occurs over a week’s time -- even though advertisers pay only for watching that happens within the first three days of telecast.

“Overnight ratings continue to disappear in relevance,” Tassler said.

Twitter: @scottcollinsLAT