Blinking colon countdown?

I’ve read this tutorial http://www.kirupa.com/developer/mx/countdown2.htm and this is the result http://dev.playon.se/countdown/index.php But if I want the 4 colons to blink say every second?

I tried to insert a new movie clip with two frames where it was visible on frame 1 and hidden on frame 2 and well it blinked with an interval of 100ms or something like that =/

So my question to you is, how can I modify the code so the colons will blink every second?

Very good tutorial btw!