How can I change the manager session expiry time?

<?php

//get the values we need to log into the mySQL server with
include 'core/config/config.inc.php';
 
//php date
$arr['php'] = date("F j, Y, g:i a");
 
//mysql
$link = mysql_connect($database_server, $database_user, $database_password);
if (!$link) {
    die('Could not connect: ' . mysql_error());
}
if (!mysql_select_db($dbase)) {
    die('Could not select database: ' . mysql_error());
}
//get the mySQL time
$result = mysql_query("SELECT NOW();");
if (!$result) {
    die('Could not query:' . mysql_error());
}
$arr['time'] = mysql_fetch_array($result);
 
//returns the system timezone.
$result = mysql_query("SELECT @@system_time_zone;");
if (!$result) {
    die('Could not query:' . mysql_error());
}
$arr['systimezone'] = mysql_fetch_array($result);
 
//returns the session timezone if it differs from the system timezone.
$result = mysql_query("SELECT IF(@@session.time_zone = 'SYSTEM', @@system_time_zone, @@session.time_zone);");
if (!$result) {
    die('Could not query:' . mysql_error());
}
$arr['sestimezone'] = mysql_fetch_array($result);
mysql_close($link);
 
$times = 'php time is: '.$arr['php'].'
';
$times .= 'mySQL time is: '.$arr['time'][0].'
';
$times .= 'mySQL system timezone is: '.$arr['systimezone'][0].'
';
$times .= 'mySQL session timezone is: '.$arr['sestimezone'][0].'
';
 
return $times;