logout user after so many minutes

hey.
ive been on several website that deal with php coding etc..
and i need help with something which the others could not help me with...
well they wuldn't reply.
here is my code at the moment
[code:1:51841318c2]
<?PHP
/// this will show weather or not their online etc...
$online = dbquery("SELECT * `members` WHERE clan='yes' AND online='1'");
$members = mysql_num_rows($online);
echo "-- Members --";
if ($members == 1) {
echo "1 online";
}elseif ($members > 1) {
echo "$members online";
}else {
echo "0 online";
}

echo "<br/>";
$online = dbquery("SELECT * `members` WHERE clan='no' AND online='1'");
$users = mysql_num_rows($online);
echo "-- Users --";
if ($users == 1) {
echo "1 online";
}elseif ($users > 1) {
echo "$users online";
}else {
echo "0 online";
}
?>
[/code:1:51841318c2]
what will happen is the user will login and in the login it will send the number 1 to the database were there username and id is.

and the script above will display how many users are online
but the only prob i have is if they forget to logout and just close there browser it will not remove the 1 from the the database.
so i thought if u culd like set a timer so lets just say the user was on the same webpage for 5 min or more and hasn't done anything then he/she will be loged out and the database will update to 0 instead of 1.

i don't know if that is possible but if it is culd someone help me please
my friend said i shuld just use a javascript to update the 1 to a 0 wen they close their browser but if they have javascript disabled then the script won't work :/

thanks for anyhelp very much appreciated

should look into cookies or sessions...