Error date NaN in firefox and IE - php

Question

Hello I need to spend a given XML through javascript to subtract the current date and time date.
What makes this code is to show the remaining time of a song streaming in minutes and seconds
And then with javascript parsing date and I transform in milliseconds and the current date will also rest in ms.
In Chrome date shows me perfectly, but in Mozilla and IE NaN console shows me and gives error.
I do not understand is that if I have parsed the date because it only works in Chrome. There must be a mistake.
PHP (I draw the start date of a song)
<?php
$xml = # simplexml_load_file('http://www.example.com');
foreach ($xml as $track){
$startTime = $track->starttime;
$songDuration = $track->playduration;
}
?>
JAVASCRIPT:
var spend javascript
var tiempoComienzo= "<?php echo $startTime ?>";
var cancionDuracion="<?php echo $songDuration ?>";
//parse delivered date from php
var d = new Date(Date.parse(tiempoComienzo));
//PHP get the date in milliseconds
var resultPHPms = d.getTime();
//get the current date
var f = new Date();
//step the current date to milliseconds
var resultJSms = f.getTime();
//adding the date of the song to the length of the song
var inicioMasCancion=parseInt(cancionDuracion) + parseInt(resultPHPms);
//It is the challenge to the current date
var TiempoRestante=inicioMasCancion-parseInt(resultJSms);
//pass the result to seconds
seconds=(TiempoRestante/1000)
var container = document.getElementById('time');
var seconds = parseInt(seconds+7);
//step seconds to minutes and seconds
var minutes = parseInt( seconds / 60 ) % 60;
var seconds = seconds % 60;
var contadorDeTiempo=(minutes < 10 ? "0" + minutes : minutes) + ":" + (seconds < 10 ? "0" + seconds : seconds);
countdown(seconds);
function countdown:
<script>
var timer;
function countdown(seconds) {
seconds--;
if(seconds >= -1) {
container.innerHTML =contadorDeTiempo;
}
}
timer = setInterval(countdown, 1000);
</script>
HTML:
<span id='time'></span>
In chrome it is perfectly displayed and works perfect. But in Mozilla and IE console NaN it is shown, specifically in this line:
var d = new Date(Date.parse(tiempoComienzo));
How I could solve? The resulting XML date is as follows:
2015-12-20 12:45:33.17
thanks very much for your help