Use click event of action link with id= "startClock"
$("#startClock").click( function(){
var counter = 5;
setInterval(function() {
counter--;
if (counter >= 0) {
span = document.getElementById("count");
span.innerHTML = counter;
}
if (counter === 0) {
alert('sorry, out of time');
clearInterval(counter);
}
}, 1000);
});