function getTime(zone, success) {
var url = 'http://json-time.appspot.com/time.json?tz=’ + zone,
ud = ‘json’ + (+new Date());
window[ud]= function(o){
success && success(new Date(o.datetime));
};
document.getElementsByTagName(‘head’)[0].appendChild((function(){
var s = document.createElement(‘script’);
s.type = ‘text/javascript’;
s.src = url + ‘&callback=’ + ud;
return s;
})());
}

getTime('GMT', function(time){
    // This is where you do whatever you want with the time:
    alert(time);
});