<script>
var timerSeconds = 20;
var interval;
function forceUpdateTimer(){
clearInterval(interval);
timerSeconds = 20;
interval = setInterval(function() {
if (timerSeconds > 0){
timerSeconds--;
$("#timerValue").text(timerSeconds);
}
}, 1000);
}
forceUpdateTimer();
</script>
<button onclick=" forceUpdateTimer();">Force update timer</button>
Calendar will update after <span id="timerValue"></span> sec
</body>