Knowing how long your talk needs to be is very important. We talked about that on day 5.
Another important component of time that I've come to really pay keen attention to is: when my talk is happening.

Speaking time-slot is as important as how long the talk needs to be. For me, it factors into the content, pace and energy of my anticipated delivery. Am I first up on the first day? Right before lunch? Right after lunch when folks get the lunch hangover? First up the morning after a big networking party with an open bar? Am I the last talk of the conference?

Whenever possible consider the time-slot, not only the talk duration, as you plot out your pace and energy for the talk you plan to give.