open phpMyadmin
open dolphin DB
open sys_injection
click sql and run this query

INSERT INTO `sys_injections` (`name`, `page_index`, `key`, `type`, `data`, `replace`, `active`) VALUES
('head_inactive_redirect', '0', 'injection_head', 'php', 'replace me', '0', '1')
INSERT INTO `sys_injections` (`name`, `page_index`, `key`, `type`, `data`, `replace`, `active`) VALUES
('body_inactive_redirect', '0', 'injection_body', 'php', 'replace me', '0', '1')

edit the created row "name = head_inactive_redirect" and replace data field with below code replacing "replace me"

if (isMember() && !isAdmin()) {
echo '<script type="text/javascript">
var timer = 0;
function set_interval()
{
timer = setInterval("auto_logout()",300000);
}
function reset_interval()
{
if (timer != 0) {
clearInterval(timer);
timer = 0;
timer = setInterval("auto_logout()",300000);
}
}
function auto_logout()
{
window.location="logout.php";
}
</script>';
}

now hit "Go"

now edit the created row "name = body_inactive_redirect" and replace data field with below code replacing "replace me"

if (isMember() && !isAdmin()) {
echo 'onLoad="set_interval();" onmousemove="reset_interval();"'
}

hit "Go" and done. I don't think i need to remind you about clear the........:) enjoy