Thanks for asking. I linked it on purpose to wikipedia from where I quote:

The meaning is sometimes used less colloquially as: "Meanwhile, the irreplaceable time escapes", expressing concern that one's limited time is being consumed by something which may have little intrinsic substance or importance at that moment.

Tempus fugit is a succint admonition to focus on what is really important as opposed to what is merely salient. Focus on the not urgent but important things(quadrant 2 in the covey matrix).

http://en.wikipedia.org/wiki/File:MerrillCoveyMatrix.png