WaitProperty waits till expire

I have written following code 

var prop=['Exists','VisibleOnScreen'],valu=[true,true];
           Log.Message("Now:" + aqDateTime.Now());
           Log.Message(MyWindow.Exists+"..........."+MyWindow.VisibleOnScreen );

          Log.Message("Now:" + aqDateTime.Now());
MyWindow.WaitProperty(prop,valu,12500);
           Log.Message("Now:" + aqDateTime.Now());

I was supposed to get MyWindow as soon as Exists and VisibleOn Screen isn't so?

But waite porpert stay untill time expires ...what could be the problem?

Pl look at my results attached