As per the following KB I made changes that should have seen timeout reduced to 2 minutes.

https://confluence.atlassian.com/pages/viewpage.action?pageId=126910597

in <confluence_install>/confluence/WEB-INF/web.xml

<session-config>
  <session-timeout>2</session-timeout>
</session-config>

I can't force Confluence to have a session timeout.

This issue has been reproduced on first a customers, my and then another engineers instance.

Workaround:

Disable all the 'Notifications' plugins that are in the Browse > Confluence Admin > Manage addons or Plugins click on 'Show System Plugins', next to the 'System Plugins'.

• Notifications and Tasks - Common Plugin
• Notifications and Tasks - Confluence Provider Plugin
• Notifications and Tasks - Host Plugin

Additionally, you will also need to disable the Confluence Quick Reload Plugin as well, to prevent calls to /rest/quickreload/ which is triggered around every 20 seconds