如何在时间轴Google图表中固定条形颜色

Question

我要根据持续时间更改时间线中特定栏的颜色，如果持续时间超过20分钟，则该栏将变为红色

<?php
  $connect=mysqli_connect("localhost","root","","agmsdb");
  if (mysqli_connect_errno()) {
    echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

  $query = "SELECT * FROM ProcessTime";
  $qresult = mysqli_query($connect,$query);
  $rows = array();
  $table = array();

  $table['cols'] = array (
    array('id' = 'Screen', 'type' = 'string'),
    array('id' = 'Movie', 'type' = 'string'),
    array('id' = 'Start time', 'type' = 'date'),
    array('id' = 'End time', 'type' = 'date')
  );

  while($res = mysqli_fetch_assoc($qresult)) {
    $result[] = $res;
  }

  foreach ($result as $r) {
    $temp = array();
    $temp[] = array('v' = $r['planeID']);
    $temp[] = array('v' = $r['ProcessName']);
    $temp[] = array('v' = 'Date(0,0,0,'.date('H',strtotime($r['StartTime'])).','.date('i',strtotime($r['StartTime'])).','.date('s',strtotime($r['StartTime'])).')');
    $temp[] = array('v' = 'Date(0,0,0,'.date('H',strtotime($r['EndTime'])).','.date('i',strtotime($r['EndTime'])).','.date('s',strtotime($r['EndTime'])).')');
    $rows[] = array('c' = $temp);
  }

  $table['rows'] = $rows;
  $jsonTable = json_encode($table);
?>

<script src="https://www.gstatic.com/charts/loader.js"   </script>
<script>
  google.charts.load('current', {
    callback: drawChart,
    packages: ['timeline']
  });

  function drawChart() {
    var dataTable = new google.visualization.DataTable(<?php echo $jsonTable; ?>);
    var container = document.getElementById('example');
    var chart = new google.visualization.Timeline(container);
    chart.draw(dataTable);
  }
</script>
<div id="example"></div>