Actually the right side graph needs a correction from my point of view. The decline in productivity doesn't happen sharply when the meeting starts. For me the decline starts between 15 to 30 minutes before the meeting slowly, as I can hardly concentrate concerned that I might miss the start. If I'm ever in hyper concentration mode, most likely I'll miss the start of the meeting.
Ah indeed, you are right, somehow I missed the unexpected part. I guess because this applies to just about any meeting to me, not only the unexpected ones so I just applied it generally x)