This article shall give you an understanding what is a session and how long does it last.
What is a session?
A session starts when the visitor opens the webpage until he closes it. In the default configuration it is limited to the current browser tab. If he opens a seperate tab, a new session starts.
There are two exceptions for it, when
Keep Session is activated in the configuration, then if a new tab is opened it joins the active session.
A session is limited to at maximum 1 hour per default, then a new session is started.