I can't tell you that - but I can tell you that I personally cancel calls 2 days in advance if there is nothing to discuss, or cut the call short 10 minutes in once it becomes clear there is nothing more to talk about.

(I want to emphasize that I'm talking about this higher-up following a Manager's schedule, not a Maker's schedule [0]. At this point in my career, I was the [suffering] adapter between the two.)

[0] http://www.paulgraham.com/makersschedule.html