Great advice from Eugene:
If someone approaches me and asks me to pronounce the invocation at an event and I say, "I don't think I should do that; I was planning to use that time to pray," the response will be, "Well, I'm sure you can find another time to do that." But if I say, "My appointment calender will not permit it," no further questions are asked. If someone asks me to attend a committee meeting and I say, "I was thinking of taking my wife out to dinner that night; I haven't listened carefully to her for several days," the response will be, "But you are very much needed at this meeting; couldn't you arrange another evening with your wife?" But if I say, "the appointment calender will not permit it," there is no further discussion.
The trick, of course, is to get to the calender before anyone else does. I mark out the times of prayer, for reading, for leisure, for silence and solitude out of which creative work - prayer, preaching, and listening - can issue." (Contemplative Pastor, 31-32.)
What things do you make a point of marking into your diary early?
H/T Al