Marketers are wondering whether Jimmy Kimmel can reset the clock on late night.

ABC is hoping to notch a few gains for Mr. Kimmel tonight when "Jimmy Kimmel Live" moves to 11:35 p.m. after years of starting after midnight. But his show is just one of at least nine now strenuously competing for viewers at an hour that once just about completely belonged to Johnny Carson. And there are more entries on the way.

ABC is portraying its move as an attempt to get better ad prices for the program -- more on that in a moment -- but the simple fact is this: As rivals Jay Leno and David Letterman draw closer to their inevitable retirements, the earlier start could help cement Mr. Kimmel as the next-best-known host in wee-hours broadcasting.

"A fresh face in late night is much needed," said Peter Gardiner, chief media officer at Interpublic Group's Deutsch agency. "I think Kimmel early will do something to draw more viewers and more younger viewers."

Drawing a bigger crowd is crucial for marketers, who in 2011 tossed approximately $733 million, according to Kantar, around those nine late-night shows. As of Dec. 23, Mr. Leno has been attracting around 3.3 million live viewers, according to Nielsen, with Mr. Letterman notching around 3 million in the same time period -- small potatoes compared to the audiences for prime-time shows such as "Modern Family" or "The Voice." But the viewers are attractive because late-night TV woos the hard-to-find 18-to-49 demographic (especially on cable). The problem is that each proliferation of late-night TV only divides its modest numbers further.

To accommodate Mr. Kimmel at 11:35 p.m., ABC is knocking aside its venerable "Nightline." "The move is critical," said Anne Sweeney, co-chair of Disney Media Networks and president of Disney/ABC Television Group, "because it's really taking advantage of the potential long-term value of the time slot."

ABC is probably right that it can get more money from sponsors by moving Mr. Kimmel earlier. TV buyers and networks are well aware that viewers drop off as the hour gets later. That's why in 2008, after so-called "commercial ratings " became the norm, NBC, ABC and CBS all made tweaks to their late-night offerings that allowed for more ads to be broadcast earlier in their shows, resulting in a shortened first segment for Mr. Kimmel and an extra ad break before midnight for Mr. Letterman.

Yet the network also sees other potential. Calling the host "an insurgent," Ms. Sweeney said "Jimmy Kimmel Live" has steadily increased its audience over the years despite its 12:05 a.m. start time. Mr. Kimmel has also embraced doing live commercials, a technique others employ but without as much gusto.

Advertisers "like him because he works with them," said Douglas Hochstadt, ABC's senior VP-late night sales and daypart planning. "He's not playing second fiddle to the established guys at 11:35."

And when David Letterman made a rare guest appearance on Mr. Kimmel's show in October, it might have been interpreted as the elder of one late-night generation passing the baton to an upstart. "I want to wish you the best of luck when you move the show," Mr. Letterman said.

There's just one problem: The odds that any single host can rebuild the late-night audience that existed even during Mr. Letterman's heyday, not to mention Mr. Carson's, seem unlikely at best. For every big broadcast effort such as NBC's "Tonight" or CBS's "The Late Show," there are multiple cable programs carving their own niche. Comedy Central's "The Daily Show" attracts fans of news and views; E!'s "Chelsea Lately" goes after young women. FX has begun airing a weekly late-night effort by comedian Russell Brand.

MTV will join the fray next fall with a weekly late-night talk show featuring comediennes Sara Schaefer and Nikki Glaser. And then there is Arsenio Hall, about to return to the late-night airwaves via a syndicated program from CBS.

"People smell blood in the water," said Brian Hughes, senior VP-audience analysis lead at Magna Global.

But Mr. Kimmel will be one of the people gamely trying to stitch up the time slot's wounds. "People watch late-night television in a regimented way," he said in an interview with Ad Age , "and I just think the idea is that people get used to the idea that I'm on at that time and I'm an option and that they become familiar with me, and, hopefully, as the sea changes, people stick with me."