GSX surely check the variables as soon as they change. But it's possible that if you set a longer (longer than the default 10 seconds ) time interval between notifications, you might still seeing the previous notification.
And, since the green bar is shared by applications, is in fact a queue, which all the messages coming from different apps stacked and queue to be displayed. So, if you have other message from other apps using the same green bar, it's possible (depending when they sent their own message), the one from GSX came later, even if it was queued when the door was still really open. There's just nothing we can do about this.