who is online

Hello.
if a user doesnt do nothing on my web site, after 5 minutes he goes offline.
(in the online block) but i want to change the interval to 30 minutes or even more.
how do i do it?
thanks
if a user doesnt do nothing on my web site, after 5 minutes he goes offline.
(in the online block) but i want to change the interval to 30 minutes or even more.
how do i do it?
thanks