dawnerd

setInterval(function() {
  console.log([s = [86400000, 3600000, 60000, 1000]][0].map(function(t) {
      return ("0" + [(t===s[0] && (remaining = (future - ~~(+new Date()/1000))*1000)), left = ~~(remaining/t), remaining -= left*t][1]).slice(-2);
  }).join(':'));
}, [1000, future = +new Date()/1000 + 100000][0]);