jQuery Countdown Timer

HTML

<div id="timer"> <span id="days"></span>days <span id="hours"></span>hours <span id="minutes"></span>minutes <span id="seconds"></span>seconds</div>

JavaScript

var timer;
var then = '2015-07-15 17:29:31';
var now = new Date();

var compareDate = new Date(then) - now.getDate();
timer = setInterval(function () {
    timeBetweenDates(compareDate);
}, 1000);

function timeBetweenDates(toDate) {
    var dateEntered = new Date(toDate);
    var now = new Date();
    var difference = dateEntered.getTime() - now.getTime();

    if (difference <= 0) {

        // Timer done
        clearInterval(timer);

    } else {

        var seconds = Math.floor(difference / 1000);
        var minutes = Math.floor(seconds / 60);
        var hours = Math.floor(minutes / 60);
        var days = Math.floor(hours / 24);

        hours %= 24;
        minutes %= 60;
        seconds %= 60;

        $("#days").text(days);
        $("#hours").text(hours);
        $("#minutes").text(minutes);
        $("#seconds").text(seconds);
    }
}