The urgency for Mr. Zucker to fix CNN became more pressing after its parent, Time Warner, rejected a takeover effort by 21st Century Fox this summer. Time Warner must now prove to its shareholders that it can grow on its own and deliver profits. As a result, the company’s Turner Broadcasting System division, which includes CNN, is in the middle of job reductions and other cost-cutting initiatives.

Jeffrey L. Bewkes, the chief executive of Time Warner, said during a recent investor call that he was excited about the evolution at CNN “but there’s still a lot more to do.”

One change that Mr. Zucker has made is emphasizing breaking news, focusing coverage on just two or three major stories throughout a given day, rather than delivering an all-encompassing, scattershot report of the headlines as was common in the past. The rationale is that viewers are likely to catch other news on the web or on social media. Mr. Zucker leads daily news meetings, unlike past CNN chiefs who delegated the responsibility. Employees called Mr. Zucker a micromanager and said that he sent missives from his BlackBerry at all hours about everything, be it the length of story segments or the graphics that appear on screen.

On Thursday, that approach meant the Ebola outbreak and the Secret Service controversy dominated airtime. This year, CNN was mocked for committing near wall-to-wall coverage to the disappearance of Malaysia Airlines Flight 370, but Mr. Zucker has boasted that the network posted better ratings than its rivals during that stretch.