DM does not log you out automatically. There is no session timeout.
Once logged in DM creates a session in its webserver. The session ID is hold in a cookie. The cookie is a “session cookie”, that is it has no expiration date. So your session is only lost when a) restarting the DM server (in particular its web server), or b) when you restart the browser (or delete the cookie manually).
In case you have installed DM integration with SAlly, then you may experience an automatically log out, to change it you must put
in Karaf’s etc/system.properties file (gives 120 minutes to time out).