Cache::FileCache can make this easy.

# from a CGI script which times users out after an interval

require Cache::FileCache;
my $cache = new Cache::FileCache({
        default_expires_in => '60 minutes',
        auto_purge_interval => '4 hours',
        auto_purge_on_set => 1,
        filemode => 0077,
        namespace => 'cookies',
        username => 'www',
}) or die "cookie_cache\n"; 

my $user = $cache->get($browser);  # logged-in user or undef

if ( defined $user and defined $q->param('_logout') ) {
        $q->delete('_logout');
        $cache->remove($browser);  # clear cache
        print($q->p("You are no longer logged in as $user."));
        undef $user;
} elsif ( not defined $user and defined (my $try_user = $q->param('_us
+er')) ) {
        $q->delete('_user');
        my $try_password = $q->param('_password');
        $q->delete('_password');
        if ( $try_user =~ /^[a-z]{1,8}$/ and verify($try_user,$try_pas
+sword) ) {
                $user = $try_user;
                print($q->p("Welcome back $user."));
        } else {
                print($q->p("I'm sorry, that's not right."));
        }
} 

if (defined $user) {
        $cache->set($browser,$user);  # reset the timeout
        # do a logout form
} else {
        # do a login form
}
...
[download]

to limit the program to running at most once per minute, try and get your entry, if you can it's been less than a minute so notify user and exit, if you can't get your entyr it's been more than a minute so do your stuff and set a new entry. you can do the same for each user and give them 1 run a minute or less than 5 runs per 20 minutes without too much work.