Shell in a box timeout?

[Automatic]

Because I'm lazy I often forget to do a proper close of the shell session using shell in a box (typing "exit") and just close the tab instead, however, this blocks up programs when I later come to use them (Mainly screen, it complains about another client already being attached to it).

 

Does anyone know how to set shell in a box to timeout after ~ five minutes of inactivity?

 

EDIT:- oh, and it does seem (or so their wiki page says) have a timeout, although, it doesn't seem to close the bash session (I have to go and kill the bash session so that I can assess screen again).