Max for webstore is 20 mins
https://386782-sb2.app.netsuite.com/app/help/helpcenter.nl?fid=section_1534882804.html
It can be decreased from the Idle Session Timeout in Minutes setting:
Setup > Company > Preferences > General Preferences
https://386782-sb2.app.netsuite.com/app/help/helpcenter.nl?fid=section_1534882691.html