Understanding Organisations by Charles Handy
Chapter 11 - On Being a Manager
"Rosemary Stewart, studying 100 managers, found that in four weeks each of them had, on average, only nine periods of half an hour without interruption, which is less than one every other day. Mintzberg, studying chief executives, found what might be called the 'ten minute itch': everything, even desk work and tours of the plant or office, seemed to get fitted into average bursts of around ten minutes except for scheduled meetings, although even these, on average, lasted only just over an hour."
Hmmmmmm sounds so familiar.