You can try somethink like this, and make o popup for asking user, simple example on fiddle
(function () {
var timeToWaitInSeconds = 10;
function countdown(){
console.log(timeToWaitInSeconds);
timeToWaitInSeconds -= 1;
if (timeToWaitInSeconds>0){
setTimeout(countdown,1000);
}
}
setTimeout(countdown,1000);
}());