Im looking for a simple count down time

Hi guys.

Im looking for a simple time that counts down the time to a certain date. and when it times out i want the script to fade out the counter and start a movie clip.

I set up a dynamic text field with an instant name of time_txt and i want the format to be in 000:00:00:00 days hours mins and seconds…

does anybody know how to right a simple action script for this?