Countdown number from PHP

programming flash
1

I have been successful to the point where I actually see the txt_hoursleft, txt_minutesleft, txt_secondsleft on a dynamic text field:

onClipEvent (load) {
    loadVariables("servertime.php", this);
}
onClipEvent (data) {
    txt_hoursleft = unescape(this.serverHours);
    txt_minutesleft = unescape(this.serverMinutes);
    secondsLeft = unescape(this.serverSeconds);
    seconds = int(secondsLeft);
    txt_secondsleft = seconds;

How do i make it countdown? An example with txt_secondsleft would help me understand. Lets say I got from the PHP file 34 secs.
I want it to show on the .swf 34 changing to 33 changing to 32… and so on.

Please help! thanks