Problem with Session Timeout

I am using Tomcat 5.5
I have the following piece of code.

session.setMaxInactiveInterval(60) ;

In this case, the session times out after 1 min.

session.setMaxInactiveInterval(39600) ;

which indicates that the session would be timed out after 11 hours of inactivity.

But, this never happens and even after 11 hours of inactivity I can still use the application.

I have tried setting this to 3600 sec (1 hr)... but it doesnt work here too.

Can somebody tell me why is it so?