Changing displayed elements of a KML file based on current system time in Google Earth

Question

Is there any way to have Google Earth turn features in a KML file on and off automatically based on the current system time? I have created the simple example below of a rectangle with a <TimeStamp> set to end before now, but it displays anyway when I load the file. If I set it for a minute or so in the future then load it and wait, the rectangle doesn't disappear when the system clock rolls past the specified end time.

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<kml xmlns="http://earth.google.com/kml/2.2">
<Document>
  <Placemark>
    <TimeSpan>
      <end>2013-07-30T22:38:00Z</end>
    </TimeSpan>
    <Polygon>
      <extrude>0</extrude>
      <tessellate>1</tessellate>
      <altitudeMode>clampToGround</altitudeMode>
      <outerBoundaryIs>
        <LinearRing>
          <coordinates>
            -10,10
            -10,-10
            10,-10
            10,10
            -10,10
          </coordinates>
        </LinearRing>
      </outerBoundaryIs>
    </Polygon>
  </Placemark>
</Document>
</kml>