简单的时间函数，计算等待时间

我试图获得一个简单的时间函数工作使用PHP来计算病人的等待时间。到达时间作为TIMESTAMP成功地输入到患者表中;这是一段代码;

// validate arrival time 
$date_time=date('Y-m-d H:i:sa');
clock time
date_default_timezone_set('Europe/London');
$the_time1 = date('G:ia');

等待时间为(时钟时间-到达时间)

然而，这在我的代码段中不起作用!

<?php
$conn = mysqli_connect("localhost","root","") or die ("No connection");
mysqli_select_db($conn, "a&e") or die('Could not select database.');
$query = "SELECT PatientID, Forename, Surname, Gender, Illness, Priority, Arrival_Time FROM Patient";
$result = mysqli_query($conn, $query) or die("Invalid query");
date_default_timezone_set('Europe/London');
$the_time1 = date('G:ia');
$date_time=date('Y-m-d H:i:sa');
echo Waiting_time($the_time1, $date_time); 
function waiting_time ( $the_time1, $date_time) {
$time_diff =  ( $the_time1, $date_time); {
$days      = floor( $time_diff / 86400 ); // 60 * 60 * 24 = number of seconds in a day
$time_diff -= $days * 86400;
$hours      = floor( $time_diff / 3600 ); // 60 * 60 = number of seconds in a hour
$time_diff -= $hours * 3600;
$mins       = floor( $time_diff / 60 ); // 60 = number of seconds in a minute
return( $days . ' days, ' . $hours . ' hours, ' . $mins . ' minutes' );
}

echo "<table border='1'>
<tr>
<th>PatientID</th>
<th>Forename</th>
<th>Surname</th>
<th>Gender</th>
<th>Illness</th>
<th>Priority</th>
<th>Waiting Time</th>
</tr>";
}
  echo "<tr>
  <td>" . $row[0] . "</td>
  <td>" . $row[1] . "</td>
  <td>" . $row[2] . "</td>
  <td>" . $row[3] . "</td>
  <td>" . $row[4] . "</td>
  <td>" . $row[5] . "</td>
  <td>" . $waitTime . "</td>
  </tr>";
  }
echo "</table>";
mysqli_close($conn);
?>

编辑;

我现在把代码改成这样;

<?php
$conn = mysqli_connect("localhost","root","") or die ("No connection");
mysqli_select_db($conn, "a&e") or die('Could not select database.');
$query = "SELECT PatientID, Forename, Surname, Gender, Illness, Priority, Arrival_Time as Waiting_Time FROM Patient";
$result = mysqli_query($conn, $query) or die("Invalid query");
date_default_timezone_set('Europe/London');
echo "<table border='1'>
<tr>
<th>PatientID</th>
<th>Forename</th>
<th>Surname</th>
<th>Gender</th>
<th>Illness</th>
<th>Priority</th>
<th>Waiting_Time</th>
</tr>";
 while ($row = $result->fetch_object()){

  echo "<tr>
  <td>" . $row->PatientID . "</td>
  <td>" . $row->Forename . "</td>
  <td>" . $row->Surname . "</td>
  <td>" . $row->Gender . "</td>
  <td>" . $row->Illness . "</td>
  <td>" . $row->Priority . "</td>
  <td>" . $row->Waiting_Time . "</td>
  </tr>";
}
echo "</table>";
mysqli_close($conn);
?>

现在显示的数据如下:

PatientID Forename Surname Gender Illness     Priority Waiting_Time 
249       Sara     Kearns  F      Immediate   high     2013-03-20 22:18:01

我需要等待时间以小时为单位显示，例如:1:15:23