Countdown

<!DOCTYPE HTML>
<html>
<style>
#time {
    color: white;
    font-family: Arial;
    font-size: 100px;
}
</style>
<script>
function startTimer(duration, display) {
    var timer = duration, minutes, seconds;
    var intv = setInterval(function () {
        minutes = parseInt(timer / 60, 10);
        seconds = parseInt(timer % 60, 10);

        minutes = minutes < 10 ? "0" + minutes : minutes;
        seconds = seconds < 10 ? "0" + seconds : seconds;

        display.textContent = minutes + ":" + seconds;

        if (--timer < 0) {
        clearInterval(intv);
        }
    }, 1000);
}

window.onload = function () {
    var time = parseInt(window.location.hash.substring(1)),
        display = document.querySelector('#time');
    startTimer(time, display);
};
</script>
</html>
<body>
<div id="time"></div>
</body>
</html>