In NT 12.12
as long as you have the client-side session manager activated (typically in the footer procedure)
and the user is logged in, and _not_ on the default page,
you can do
p_web.script('$("#counter").ntsessionmanager("setTimeOut","140");')
where 140 is the number of seconds you want the session to be alive for.
140 is more of a "guide" - it will always round up to a multiple of the server-side-timeout value.
So if your server side timeout is say 5 minutes, this effectively sets it to 5 minutes, 10 minutes, 15 minutes or whatever.
cheers
Bruce