How to display alert when system time is equal to time fetched from database?

How to display alert when system time is equal to time fetched from database?

What I want to know is there any way when ($res[6] == system time),it
would display an alert saying "you've got a callback",that will display
until OK button is pressed. Any help is greatly appreciated...Thanks in
advance
<table border="1" cellspacing="1" cellpadding="1" width="100%" >
<tr>
<td align="center" valign="top" width="20%">Customer Name </td>
<td align="center" valign="top" width="20%">Callback Date </td>
<td align="center" valign="top" width="20%">Callback Time </td>
<td align="center" valign="top" width="20%">Contact Number </td>
<td align="center" valign="top" width="10%">Edit </td>
<td align="center" valign="top" width="10%">Delete </td>
</tr>
<?php
include("config.php");
$sql = "Select * from callback where userid='$agent_id'";
$result = mysql_query($sql);
while($res = mysql_fetch_array($result))
{
if($res[7] == '0')
{
?>
<tr>
<td align="center" valign="top" width="20%"><?php echo $res[4] ?></td>
<td align="center" valign="top" width="20%"><?php echo $res[5]; ?></td>
<td align="center" valign="top" width="20%"><?php echo $res[6]; ?></td>
<td align="center" valign="top" width="20%"><?php echo $res[9]; ?></td>
<td align="center" valign="top" width="10%"><a
href="editcallback.php?id=<?= $res[0];?>">edit</a></td>
<td align="center" valign="top" width="10%"><a
href="deletecallback.php?id=<?=$res[0];?>"
onclick="ValidateOnDelete()">delete</a></td>
</tr>
<?php }
else
{
?>
<tr bgcolor="#F2CBC9">
<td align="center" valign="top" width="20%"><?php echo $res[4] ?></td>
<td align="center" valign="top" width="20%"><?php echo $res[5]; ?></td>
<td align="center" valign="top" width="20%"><?php echo $res[6]; ?></td>
<td align="center" valign="top" width="20%"><?php echo $res[9]; ?></td>
<td align="center" valign="top" width="10%"><a
href="editcallback.php?id=<?= $res[0];?>">edit</a></td>
<td align="center" valign="top" width="10%"><a
href="deletecallback.php?id=<?=$res[0];?>"
onclick="ValidateOnDelete()">delete</a></td>
</tr>
<?php
}
}
?>
</table>