In the past 15 years, the number of households that have a TV set on at 4:30 has doubled, to 16 percent this year from 8 percent in 1995. At 11:30 p.m., by comparison, when most local newscasts end, 44 percent of televisions are on, up 10 percent from the levels 15 years ago.

And although all TV newscasts skew toward older demographics, in New York, the percentage of viewers under 35 watching from 3 a.m. to 5 a.m. is higher than at any other time of day, an important part of the advertising pitch for an industry that chases young people. “We’re going to where the viewers are,” said Dave Davis, the general manager of WABC in New York.