Session TIme out in Websphere

HTTP Session time-out Override Precedence Summary

The list below shows the precedence from which the final HTTP Session time-out is derived.

1. Server Level Lowest level
2. Enterprise Application Overrides the Server Level if Override is selected
3. Web Application Overrides the Server and Enterprise Application settings if Override is selected
4. Application Level (web.xml) Overrides Server, Enterprise Application, and Web Application settings
5. Application Code Overrides all other settings

In conclusion, we can load session timeout from local db and overide using application code.

For more info, refer  IBM support