Where does classic ASP store the value for session timeout? I have looked through the code and this classic ASP website isn\'t using Global.asa(so no \"Session_OnStart\") or
You can do it 2 way.
Put global asa file into root of your site and define session time out there
You can introduce following line on top of each of the pages in question (if you not using include header)
<%
Session.Timeout=20
Server.ScriptTimeout=1200
%>
20 is been period in minutes and 1200 is same period in seconds. Keep in mind that server takes a seconds not a minutes!!! By default IIS terminates any script if it runs longer then 90 seconds.
If you using include file as a header then you will need to do it only once there, on the top of the page right after option explicit. and assuming that you already did disabled all app pool defaults as what @Lankymart suggested.