I'm still reading my way through Bill Hybel's Axioms and then came across one I've been using a bit recently. It goes, 'If you're going to have a silly day have a very silly one.'
In other words if a day looks so busy you will never get any study/desk/admin. time in the gaps between the appointments then maximise the appointment time. Fit a couple of half hour appointments in the gaps.
Bil Hybels breaks his day into fifteen minute chunks. Lord knows how small the chunks of say, a President or Prime Minister are.
My first ministry boss used to say, 'I've got a whole half hour.' Twenty five years on I think I understand at last.