Not so long ago, the broadcast networks trumpeted the shows in the final hour before the news — 10 p.m. Eastern time (9 p.m. in Hawai'i) — as "appointment viewing," an hour so named for its slate of sophisticated and stylish dramas that commanded a rapt audience who watched in real time.

Today, audiences are still watching in that final hour, but often not what the networks programmed for that time slot.

Instead, people are increasingly playing back recorded shows from their digital video recorders.

"Essentially the DVR has been like adding a whole new competitor to the time period," said David Poltrack, CBS' chief research officer. "The new competitor is often our own programming."

More than 36 percent of all TV households now are equipped with a DVR, accelerating shifts in viewing patterns. In the final-hour time slot, nearly 6 million viewers are watching previously recorded shows, according to ratings firm Nielsen Co. On Friday night, for example, as many people are watching recorded shows as the top program in the time period, "Numb3rs" on CBS, Poltrack said.

NBC's ratings are down 27 percent during the time slot compared with last season among advertisers' favorite demographic, 18- to 49-year-old viewers.

Ratings for ABC are down 11 percent during that time slot, compared with the 2008-2009 TV season, and CBS is off 3 percent.

Alan Wurtzel, NBC Universal's president of research and media development, said the use of DVRs "puts additional pressure on programs to be compelling. Now shows also have to compete with a disc full of shows that are, by definition, people's favorites."

Still, the TV executives say, the effects of digital recorders haven't been all bad.

"The DVR is kind of a frenemy," said Wurtzel. "It throws up into the air 50 years of established behavior when we didn't have the ability to fast-forward through commercials. But DVRs also extend the reach and the audience for many of our shows."

Overall, DVR playbacks have dramatically increased the audience for certain shows, including "Grey's Anatomy" on ABC, "The Mentalist" on CBS and "Vampire Diaries" on the CW. Digital recorders tend to give the biggest lift to the most popular shows and those with younger-skewing audiences.

"Big shows get even bigger," Poltrack said. And the weaker shows get hurt.

The final hour of prime time is of particular importance to the networks and their TV stations because it serves as a funnel or lead-in to their local news.

This fall, there will be more new shows on in the final hour than in any other time slot. NBC plans to order four are slated for the time slot, including "Chase," from Jerry Bruckheimer about U.S. Marshals, and a "Law & Order" spinoff set in Los Angeles. The network is also bringing back its Tuesday drama "Parenthood."

ABC also will have a couple of new shows on in the time slot, including "Detroit 1-8-7," a police drama done in documentary style starring Michael Imperioli from "The Sopranos."

CBS has three new high-profile projects for the time slot, including a remake of "Hawaii Five-0" and a legal drama called "The Defenders" about Las Vegas lawyers.