PHP help - Using Date?

Hey,

I know the title is a little vague but anywho!

Im currently making an alert script, when the alert is submitted to the MySQL DB it logs the time it is sent in a field called "time"

Now I am trying to make it so the alert only shows for a period of lets say a second for a user alert and then a minute for a sitewide alert?

How do I get it to only display if it is within this time? Also how could I make it so only two alerts could be sent per hour?

Im not exactly the best at explaining what I mean lol :P

PHP Code:

---

<?PHP

/*
* @copyright 2008
*/

include_once 'includes/php/config.php'; // Includes the User System Config
include_once 'includes/php/radio_dj.php'; // Includes the Radio Config File (To get current DJ)

    echo '<span class="SUBHEADLINE">Send an Alert!<br />
    </span><em>Alert a specific user! (Only the current DJ can send)</em><br /><br />'; // Header Echo :)
    
        switch ($_GET[sent]) { // Specifies how the switch class works - In this case ?sent=
            default: // Obvious, Sets the default page
            
                if ($logged[user] == $servertitle || $logged[level] == 11) { // Checks if you are DJing or Admin
                    echo '<font color="#009900"><strong>You are the current DJ - Alert a user below:</font></strong>        
                            <br><br>';
                            
                    echo '<form method="post" action="?page=useralert&sent=yes">
                            <table border="0" cellpadding="2" cellspacing="2">
                              <tr>
                                <td>Username:</td>
                                <td><input name="username" type="text" id="username" size="20" maxlength="20"/></td>
                              </tr>
                              <tr>
                                <td>Alert: </td>
                                <td><input name="message" type="text" id="message" size="70" maxlength="100"/></td>
                              </tr>
                              <tr>
                                <td>&nbsp;</td>
                                <td><div align="right">
                                  <input type="submit" name="send" id="send" value="Send Alert">
                                </div></td>
                              </tr>
                            </table>
                            </form>';
                                
                            }
                else {
                    echo '<strong><font color="red">You are not the current DJ - This can only be used by the online                             DJ!</strong></font>';
                    }    
                    
            break; // Break the page!
            
            case 'yes':
            
                if ($_POST[send]) {
                    if($_POST['username'] == ""|$_POST['message'] == ""){
                    echo "<strong><font color='red'>You have missed out something, <a href='?page=useralert'>Go back</a> and try again!</font></strong>";
                    }else{    
                if($_POST['username'] == "ALL"){
                

                    $message = $_POST[message];
                    $sentfrom = $logged[username];
                    $sendto = $_POST[username];
                    $senttime = date('H:s');
                    $sentdate = date('d/m/y');
                    $query = "INSERT INTO alert (name, message, sentfrom, ipsent, time, date)                                   VALUES('$sendto','$message','$sentfrom','ALL', '$senttime','$sentdate')";
                    mysql_query($query) or die(mysql_error());
                    echo "<font color='#009900'><strong>Your alert has been sent to everyone!</strong></font><br>The alert was: <strong>$message</strong>";
                    }else{
                    
                    $ipsendto = mysql_query("SELECT * FROM users");
                    $ipsend = mysql_fetch_assoc($ipsendto);
                    $message = $_POST[message];
                    $sentfrom = $logged[username];
                    $sendto = $_POST[username];
                    $senttime = date('H:s');
                    $sentdate = date('d/m/y');
                    $query = "INSERT INTO alert (name, message, sentfrom, ipsent, time, date)                                   VALUES('$sendto','$message','$sentfrom','$ipsend[last_ip]', '$senttime','$sentdate')";
                    mysql_query($query) or die(mysql_error());
                    echo "<font color='#009900'><strong>Your alert has been sent to $sendto!</strong></font><br>The alert was: <strong>$message</strong>";
                    }
                    }
                                        
                }            
                // Do this next :)
                
            break;
}
?>

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I know its not the best code in the world lol, this is the code to submit it to the database, not view the alert

php.net/time?

Found another way to do it, Reason I wanted this was so it was like a log - Just going to log separately now.

Thanks anyway!