My first semester of graduate school, I took a course taught by the woman who would eventually become my dissertation director. In our first class meeting, we signed up to do 10-minute presentations on certain contextual materials, one or two per week. My friend Ted volunteered to go first, at our very next meeting.
In what I would soon learn was characteristic fashion, Ted spent the intervening week reading his assigned text and an ad hoc collection of background materials, and he showed up for class with an armful of notes and photocopied images. He launched into a chatty but meandering presentation, pausing to share colorful anecdotes about the author's life, theories about the circumstances of the work's composition, and other more or less interesting digressions.
After several minutes, our professor interrupted him: "Ted, you've wasted five minutes. You have five more. Let's get to the text itself."
"Of course, of course," he said, agreeably--and he may have attempted to focus or speed himself up, but it wasn't apparent.
Our professor gave him another warning, at the two-minute mark, but when his ten minutes had expired without his having done more than allude to the work he was supposed to be presenting on, she cut him off mid-sentence.
"Well," she said, as she reclaimed the room. "I hope this will be a lesson to all of you. When you have ten minutes, you have ten minutes. You should prepare accordingly."
It was a fairly awful thing to do to a student in his second week of a Ph.D. program, in front of his entire cohort, but it had its intended effect: we learned that time and page limits were to be taken seriously--and that being smart and having lots to say didn't make us special or exempt us from the rules.
Whether it was my professor's doing or my own already-fierce ethic of responsibility, I now consider going long to be a pretty serious crime, at least when there's a captive audience of listeners or readers. My belief is that an extra 10% (which amounts to one extra page or two extra minutes on a conference paper) might be okay, depending on the circumstances, but anything more is a sign of astonishing disorganization, self-importance, and/or lack of regard for one's audience.
Recently, however, I was in a scholarly situation where more than half of the participants (all of them faculty) exceeded their time/page limits by an absolutely egregious amount--I'm talking about an extra 30%, 50% or in one shocking case a full 100%.
It's not that their work wasn't good; in some cases, it was very good. But when I (and you) sign up for the X-length version of your work, I don't want the Y-length version.
Some day, I'll have the balls to walk out, interrupt, or stop reading when time expires.