See my suggestion above clarkwinkelmann that allows you to customize the session duration for users who don't use the "remember" feature.
luceos I never had any issue staying logged in
If you enable "remember me", then the session never really expires (it boots again from the remember cookie automatically). I rarely not use the remember feature, but I tested locally and the session does expire after 2 hours. If the Flarum tab is kept open during that time, strange things can happen if you try to start a new discussion or reply to the currently open discussion.