For many years, Don Imus, the oh-so-modest radio talker, has signed off his syndicated morning program with an announcement that the revenue-producing portion of the station's broadcast day has just ended. At many stations, Imus's jab comes uncomfortably close to the truth.

But why does 6 to 10 a.m. account for such a disproportionate share of radio's profits and promotions? Don't just as many people go home from work in the afternoon as commute to work in the morning?

Yes, but listeners' needs are different in the morning, radio executives say.

In the morning, people want "an information fix," says Lee Abrams, chief programming officer at XM Satellite Radio and a veteran of traditional broadcast radio. "What happened in baseball last night? What's the forecast today? What did I miss? People are conditioned to getting that fix in the morning more than the afternoon, when a 'wind-down' mentality often sets in."

WPGC (95.5 FM) is a good example of a station that has a more information-heavy approach in the morning, with its "Donnie Simpson Show," than it does in afternoon drive time.

Since listeners are assumed to be paying closer attention in the morning, it makes sense for stations to focus their top talent on that part of the day. On Majic 102.3, the syndicated "Tom Joyner Show" leads off the day, while the station turns to a far less well known local DJ, Alvin John Waples, for afternoon drive time. On WDMV (700 AM), the "Greaseman," Doug Tracht, brings a well-lubricated touch of creativity and celebrity to the morning shift, while the afternoon commute is left to the likes of the Congressional Funding Mortgage Hour.

Still, there are plenty of exceptions to the notion that morning rules, and Walter Sabo, an influential consultant to talk stations, notes that many of radio's biggest stars work after 10 a.m., including the nation's most popular radio talker, Rush Limbaugh; advice talker Laura Schlessinger; and Washington's afternoon bad boys, Don and Mike, whose program regularly outdraws WJFK-FM's morning offering, "The Howard Stern Show."

"Historically, many of the most famous DJs worked afternoon drive," Sabo says, adding that "at many stations, the highest-paid talent is the p.m. drive host or jock."

But in most of radio, the sun shines brightest in the morning, in part because morning listening is more compressed than it is at the end of the day, giving stations a big bulge of listeners to sell to advertisers from 7 to 9 a.m., when the morning commute is most tightly jammed. (The Washington area, however, stands out for traffic congestion that starts by 6 and continues until 10.)

Bennett Zier, regional vice president of Clear Channel Radio, which owns eight stations in the Washington area, argues that morning radio "is important not because there are more people listening, but because it's the point of entry for most radio stations. If you tune in first thing in the morning and you like what you hear, you're likely to stay for the day."

That factor is especially important for stations that try to appeal to at-work listeners. Stations such as classical WGMS (103.5 FM) and light pop WASH (97.1 FM) move from personality-oriented morning shows to music-heavy midday programming to land listeners on their way to work and keep them throughout the day. "As they say in the cereal business," Zier notes, "breakfast is the most important meal of the day."

In A.M. drive time, WMMJ gets the revenue flowing with Tom Joyner.Rise and shine: During the lucrative morning hours, stations often showcase their top talent, such as Doug "Greaseman" Tracht, above, at WDMV, and Donnie Simpson, left, at WPGC. Don Geronimo and Mike O'Meara, with their hit afternoon show on WJFK, are among the exceptions to the rule.