Countdown by mbostock

index.html

<!DOCTYPE html>
<meta charset="utf-8">
<style>

#countdown {
  font: 100px/500px Menlo;
  text-align: center;
  width: 960px;
}

</style>
<div id="countdown"></div>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var formatTime = d3.time.format("T-%X"),
    countdown = d3.select("#countdown"),
    today = d3.time.day(new Date);

// 9 AM tomorrow
var deadline = d3.time.day.offset(today, 1);
deadline.setHours(9);

(function tick() {
  var now = new Date;
  countdown.text(formatTime(new Date(+today + +deadline - d3.time.second(now))));
  setTimeout(tick, 1000 - now % 1000);
})();

</script>