I think using the numbers effect and just keyframe the numbers and uncheck proportional spacing and you should be good to go. One think about the number effect is when you turn off decimals, it rounds the result. For instance if you had a 60 second composition and you wanted to countdown from 60 to 0, you would need to start at 60.5 and go to 0.
Another more accurate way to do this would be to use a counting expression. I got this from Dan Ebberts int the expressions forum. First create a new comp the length you need to countdown and create a text layer by pressing “cntl+alt+shift+T”. Twirl open the empty text, twirl open text and “alt+click” Source Text and paste the following(to adjust your countdown adjust the clockStart variable):
rate = -1;
clockStart = 60;
function padZero(n){
if (n < 10) return "0" + n else return "" + n
}
clockTime = Math.max(clockStart + rate*(time - inPoint),0);
t = Math.floor(clockTime);
min = Math.floor((t%3600)/60);
sec = Math.floor(t%60);
min + ":" + padZero(sec)
Johnny Cuevas, Editor
Thinkck.com
“I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work.”
—THOMAS EDISON on inventing the light bulb.