<div class="counter" id="counter">
<div class="timer">
<span id="days"></span>
дн
</div>
<div class="timer">
<span id="hours"></span>
час
</div>
<div class="timer">
<span id="minutes"></span>
мин
</div>
<div class="timer">
<span id="seconds"></span>
сек
</div>
</div>

$(document).ready(function(){

var end = new Date("2019/10/31 00:00:00");

var _second = 1000;
var _minute = _second * 60;
var _hour = _minute * 60;
var _day = _hour * 24;
var timer;

function showRemaining() {
var now = new Date();
var distance = end - now;
if (distance < 0) {
clearInterval(timer);
document.getElementById('counter').innerHTML = 'Время вышло!';
return;
}

var days = Math.floor(distance / _day);
var hours = Math.floor((distance % _day) / _hour);
var minutes = Math.floor((distance % _hour) / _minute);
var seconds = Math.floor((distance % _minute) / _second);

document.getElementById('days').innerHTML = days;
document.getElementById('hours').innerHTML = hours;
document.getElementById('minutes').innerHTML = minutes;
document.getElementById('seconds').innerHTML = seconds;
}

});