Script do not count time zones. So for me fresh updates looks as 4h-old ones. I think will be easier to recieve age of spotted char from server so no need to mind client time zone.
Timezone should not be a problem as all date are passed to client with the time offset on it, your browser should automatically display it with your timezone.
I think you misunderstood how datas are shared => Even if you get the most recent data if the other guy uploaded 4 hours ago the data will be 4 hours old.
Try to do it just after your teammate uploaded his line of sight.
If you still have problem with the time displayed then we have a bug.