title: flutter - how to best practice make a countdown widget
body: <p>Im developing a soccer match schedule application <a href="https://i.stack.imgur.com/CmpG5.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/CmpG5.png" alt="see image"></a>. 
  I want to add a countdown when kick off the match.
  How to best practice make a countdown widget with the format hh : mm : ss ?</p>