How long is your :
Default DHCP lease time ?
Max DHCP lease time ?
concerning your interfaces interfaces ?
You are using a captive portal on LAN and OPT1 ?
Btw : Captive portal users are 'DISCONNECTED' by the function captiveportal_prune_old() (/etc/inc/captiveportal.inc)
Note : a "idletimeout" of 7200 minutes should NEVER log you out (= DISCONNECT). Today, every device does communicate all the time. For example, update checks are running all the time. A basic Windows system will sue the Internet - if a connection is available - all the time.
This means that the activity indicator (see Status -> Captive portal - and hit the "Show last Activity" button) will be set to a recent time all the time. A period of 5 days of NO activity at all is impossible.
This means that's something is very wrong ….
note2 : Did you checked "Status -> Captive portal - (and hit the "Show last Activity" button)" ? The Colum "Last activity" stays on recent times ?