Thanks to Ned for sharing this link to The Tyranny of email. It contains some good thought – like the three hour rule:

I maintain that programming cannot be done in less than three-hour windows.  It takes three hours to spin up to speed, gather your concentration, shift into “right brain mode”, and really focus on a problem.  Effective programmers organize their day to have at least one three-hour window, and hopefully two or three.  (This is why good programmers often work late at night.  They don’t get interrupted as much…)