Session timeout length

[Fishcake]

I'm trying to make a Session last for 2 hours but just can't seem to make it work.

i have this code in web.config

    <sessionState 
            mode="InProc"
            stateConnectionString="tcpip=127.0.0.1:42424"
            sqlConnectionString="data source=127.0.0.1;Trusted_Connection=yes"
            cookieless="false" 
            timeout="120" 
    />

and then try and set session.timeout when a session begin ie.

Sub Session_Start(ByVal sender As Object, ByVal e As EventArgs)
        ' Fires when the session is started
        Session.Timeout = 120
    End Sub

If in debug mode i use a breakpoint and check the value of Session.timeout it does indeed equal 120, yet the Session never lasts that long when i test it by leaving it alone, say for 30 mins then i come back to it run a little test that tests session values only to find the session has ended.

Anyone know any idea why this is happening?
Is 2 hours just to long to hold Session? if so why is session.timeout an integer (in minutes)?

Thanks for any help.