Hi Anutosh,
The web session value for InfoView, CMC is by default 20 mins.
So, if you want to modify that then you can edit the web.xml file for that application say InfoView under Tomcat.
Open web.xml under <BO Installdir>\Business Objects\Tomcat55\webapps\InfoViewApp\WEB-INF.
Modify session.timeout value and save the file. Restart Tomcat.
For more information on Session Management, refer the following links:
BusinessObjects Administration – Managing Sessions
Hope this helps.
-Renu