NEW YORK -- The natural rhythms of television used to be as dependable as leaves sprouting in spring and falling in autumn.
Broadcast networks would premiere new shows in mid-September, then replace failures when the weather turned cold. Summer was rerun season. Except for the occasional special, prime-time schedules rarely changed.
Those days are long gone.
Series pop up and disappear anytime, dispatched around the schedule like chess pieces. Some shows are rerun all the time, others never. You can't even count on a show to start at the top of an hour anymore.
For ABC, CBS, NBC and Fox, plus upstarts WB and UPN, the landscape is changing rapidly. The reasons include viewers' lackluster response to the current season, cable continuing to grab viewers and awards, and the hyper-competitiveness of TV executives.
For viewers, their trusted TV sets can be confusing. Here's a look at how things are changing and why:
New shows all year round
Gail Berman wants to put a sign up for Fox viewers: We never close.
The Fox entertainment president is an enthusiastic proponent of all-season scheduling -- starting new shows all the time, not just in the fall. The summer will no longer be a wasteland.
Hard lessons dictated violating one of TV's sacrosanct rules. The last few autumns have been ratings disasters at Fox because the baseball playoffs and World Series dominate its October schedule, overshadowing the fall premieres.
Most of Fox's big winners lately have originated in other seasons. "The O.C." premiered last summer. "The Simple Life" came in December. "American Idol," the real centerpiece of Fox's year, began again in January and is dominating the ratings.
NBC entertainment chief Jeff Zucker also said he would premiere many of his network's new shows this year in August, right after the Summer Olympics end.
In its infancy, television had a more year-round approach. But as live programming gave way to filmed shows, and stars began expecting summer vacations, start dates drifted toward the fall. In the early 1960s, ABC instituted a September "premiere week" to attract attention, and other networks followed suit, said Tim Brooks, co-author of "The Complete Directory to Primetime Network and Cable TV Shows."
"Once they got into the routine," Brooks says, "nobody wanted to be the one to break out of it."
Cable networks recognized the summer vacuum and filled it with their best material, siphoning viewers away from the networks. And the surprise summer success of broadcast shows like "Survivor" and "Who Wants to Be a Millionaire" upset conventional wisdom by proving people will watch TV then if there's something worth watching.
Changing the rhythm of television, however, requires altering not only viewer expectations, but the structure of a multi-billion dollar business. Many actor and writer contracts are tied to the traditional TV calendar. More importantly, networks are accustomed to presenting their fall schedules to advertisers in May to lock in billions of dollars of commercial time.
But true year-round scheduling for the networks' first-rate material also won't happen as long as summer months are considered less valuable to advertisers. Notice how CBS' "Survivor" established itself in the summer, and has never appeared there again?
Abrupt schedule shifts
NBC switched "The Apprentice" from Wednesday to Thursday after just one week, concerned that "American Idol" was making it impossible to compete. Then, when Donald Trump's boardroom game took off, NBC quickly scheduled reruns. And then CBS hurriedly put a rerun of "CSI" on against it one week to take some audience away.
You get the picture. TV schedules stay in motion as executives search for every possible advantage. A few ratings points can spell the difference between first and third place, costing advertising dollars and buzz.
"Scheduling has become such a refined art form, because there are a lot of ramifications to scheduling wrong and scheduling badly," said ABC's Braun.
TV executives are also as competitive as athletes: CBS' Moonves loves to stick it to NBC's Zucker, and vice versa. That's partly why "CSI" was deployed to derail "The Apprentice."
Zucker is a big proponent of aggressive schedule changes.
He argues that the days of viewers forming habits around TV schedules, with a few exceptions, are over. Viewers are used to choosing between hundreds of channels, DVDs and video games, he says, and are sophisticated enough to check onscreen program guides at the beginning of an evening.
Super-sized showsEver program your recorder for "Friends" or "American Idol" without realizing the network has tapped an extra 15 minutes onto the show -- and the recorder doesn't pick it up?
The super-sized show, a phrase Zucker adapted for TV, is all about money. A few extra minutes of "Friends" means a few extra minutes of ads on television's most popular comedy.
More popular now is the tendency to fiddle with starting and ending times of programs, doing anything possible to prevent viewers from using their remote controls.
One fascinating battleground is Thursdays at 9 p.m. CBS is well aware that many fans of "CSI," television's most popular show, switch networks when it's over to watch an old favorite, NBC's "ER."
So CBS frequently runs "CSI" a few minutes long. To complicate matters, NBC sometimes begins "ER" a minute or two before the hour.
Neither network wants to make it easy for a viewer to change channels. The question is whether there are repercussions to messing with the audience's viewing habits.
"There is a price you pay when you do that," Braun said. "Sometimes you evaluate it and it's worth the price."