How to get global time(not the pc time) using javascript or jquery?

Use a time API like: http://www.timeapi.org/

<script type="text/javascript">
     function myCallback(json) {
          alert(new Date(json.dateString));
     }
</script>
<script type="text/javascript" src="http://timeapi.org/utc/now.json?callback=myCallback"></script>

You can use the UTC methods from Date object: http://www.w3schools.com/jsref/jsref_obj_date.asp

var utcDate = new Date(json.dateString);
alert(utcDate.getUTCFullYear() + '-' + utcDate.getUTCMonth() + utcDAte.getUTCDate());