How Long is Too Long?

Attention spans are short these days but not everything can be summed up in 40 characters. On the flip side, how long do you have before attendees start losing focus (and patience)? I thought of this yesterday while I was locked in a room in an off-site, all-day meeting. One of the drawbacks of working for a magazine that spotlights the meetings and events industry is you pay attention to all of these tiny details that others may not even notice. Case in point? The first thing someone did in the meeting was close all of the blinds. Ugh. I find sitting in a windowless cave to be incredibly uninspiring, especially when the focus of the meeting is supposed to be brainstorming! What really got me thinking, though, was the length of the meeting. It was slated to begin at 9 a.m. and end at 5 p.m., but went almost an hour longer, and lunch was eaten without a break. By 3 p.m., I felt completely enervated. By 5 p.m., I was downright cranky. It had me thinking last night, how long is too long? Do you have a certain amount of time you aim for or do you just let meetings run as long as necessary? Do you find that most people function well for a certain block of time?