Наверно так:
<center>
<div id="countdown"></div>
<span id="span">remain</span>
</center>
CountDownTimer('<?php echo date("m/d/Y H:i A", time()); ?>', 'countdown');
function CountDownTimer(dt, id)
{
var end = new Date(dt);
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(id).innerHTML = 'EXPIRED!';
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(id).innerHTML = days + 'days ';
document.getElementById(id).innerHTML += hours + 'hrs ';
document.getElementById(id).innerHTML += minutes + 'mins ';
document.getElementById(id).innerHTML += seconds + 'secs';
}
timer = setInterval(showRemaining, 1000);
}