getTimeFromMillis.js

// converts milliseconds to '3:45' or if hours > 0, '2:01:23'
var getTimeFromMillis = function( ms ) {
  var seconds = ~~( ( ms / 1000 ) % 60 ),
      minutes = ~~( ( ms / ( 1000 * 60 ) ) % 60 ),
      hours   = ~~( ( ms / ( 1000 * 60 * 60 ) ) ),
      twoDigit = function ( n ) {
        return n < 10 ? '0' + n : n;
      },
      seconds = ':' + twoDigit( seconds );

  return hours > 0 ? hours + ':' + twoDigit( minutes ) + seconds : minutes + seconds;

};

@jfsiii: Tell a lie, I found it. Here's my slightly more verbose offering http://jsfiddle.net/codeinfront/9BFFS/ :)