Even if there's only 5 minutes worth of information, someone will always try to fill up the remaining time by talking.

I think part of the problem is that Calendar Apps insist on breaking up the selectable time into 30 minute intervals. And if true, this suggests an interesting proposition. It means that the loss in productivity from meetings is directly attributable to poor software implementation. Which means one obvious way to counter this problem is to (by default) create meetings in 5-minute intervals.