For ajax request, ServeResource is good option. Also userId and isGuest can be fetch from ThemeDisplay in server side so you do not need to pass it in request. Here is updated code :

<portlet:resourceURL var="getXXXURL" id="getXXX">
</portlet:resourceURL>
<script>
setInterval(function() {
var url = '<%=getXXXURL.toString()%>';
AUI().use('aui-base','aui-io-request', function(A){
A.io.request(url,{dataType: 'json',method: 'GET',
data: {param:"timezone"},
on: {
failure: function() { },
success: function(data) {
var data = this.get('responseData');
A.Array.each(data, function(obj, idx){
var location = obj.area;
var timeValue =obj.timeZone;
});
}
}
});
});
},60*1000);
</script>

and in Java class:

@Override
public void serveResource(ResourceRequest resourceRequest, ResourceResponse resourceResponse) throws IOException,
PortletException {
ThemeDisplay themeDisplay = (ThemeDisplay) resourceRequest.getAttribute(WebKeys.THEME_DISPLAY);
String resourceID = resourceRequest.getResourceID();
long userId = themeDisplay.getUserId();
long defaultUserId = themeDisplay.getDefaultUserId();
//do what you want to do
}