By default, the timeout of the Explorer web application is 20 minutes.
C:\SAP BusinessObjects\SAP BusinessObjects Enterprise XI 4.0\warfiles\webapps\explorer\WEB-INF\web.xml
20
We increase this value to 60 and make a similar change for the BOE application, too (BI Launch Pad and CMC).
Be sure to put the “original” and your modified web.xml in a safe place (off the server) and remember that most patches will overwrite this file (so you’ll have to put the timeout change in again).