Memory allocation per JVM in Oracle weblogic server

One of our clients has a statutory requirement of setting the time-out values of the application server(Weblogic server) at 4 hours . Oracle recommends to not use any value beyond 1 hour as it might create a lot of JVM's and might create an out of memory situation on the web servers . But our client says that the hardware configuration is capable enough to handle the 4 hours timeout value . Hence wanted to know how much memory is allocated per JVM/user session created on a web server .