How Does Connection Time Out Work?
The timeout is the browser's max idle time (browser non activity time). The activities are any activities that make a request(s) to the server, for example, clicking on a link/tab/button. Editing a WYSIWYG editor doesn't count as activity (it is the user's activity that counts).
When the browser's idle time exceeds the "timeout" set, the user will be logged out when they attempt activity. SSO users will be redirected to the home page when they click on a link, a tab or submit button. Non-SSO users will be redirected to the login page (or IDP [SSO] URL if the IDP URL is set). Prior activities (such as idea content to be submitted) performed right before the redirection happens will be lost.
The browser shares sessions among its tabs. For example, if the timeout is set to 20 minutes, you use one tab to type an idea, and another to browse the site (it doesn't matter whether you are browsing the same or different communities, as long as they are on the same site), which you use every 5 - 10 minutes while you are typing in another tab, then the browser will not time you out when you submit the idea, even though the post idea page has idled for 25 minutes.