//cdnjs.cloudflare.com/ajax/libs/moment.js/2.8.3/moment.min.js

by kougiland

HTML

<script src="//cdnjs.cloudflare.com/ajax/libs/moment.js/2.8.3/moment.min.js"></script>

JavaScript

var count_down = moment().hour(0).min(30),
    format = 'H[Stunde ]m[minute ]s[sekunde]';

if(count_down.hour() === 0){
    format = 'm[minute ]s[sekunde]';
    alert( count_down.format(format) );
}