Unity UI Making UI text, seconds pulse the last 30 seconds.

Im having a really rough time, trying o make my timer UI text pulse every second, the last 30 seconds of my game round. Im not very familiar with text UI, so i thought i could make a neat little animation, but it turns out i cant.
Any help would be apreciated, thanks for your time

 

I usually code my animations (if they are simple).
but you can also use a library for create animations from code like iTween.