Bounce rate is single-page sessions divided by all sessions, or the percentage of all sessions on your site in which users viewed only a single page and triggered only a single request to the Analytics server.
These single-page sessions have a session duration of 0 seconds since there are no subsequent hits after the first one that would let Analytics calculate the length of the session. Learn more about how session duration is calculated.
<script type="text/javascript">
(function (tos) {
window.setInterval(function () {
tos = (function (t) {
return t[0] == 50 ? (parseInt(t[1]) + 1) + ':00' : (t[1] || '0') + ':' + (parseInt(t[0]) + 10);
})(tos.split(':').reverse());
window.pageTracker ? pageTracker._trackEvent('Time', 'Log', tos) : _gaq.push(['_trackEvent', 'Time', 'Log', tos]);
}, 10000);
})('00');
</script>