D-Link routers do not have a setting to set the time out to log a user off. I believe the time defaults to 3 minutes of inactivity then logs you out. I asked about this a long time ago and D-Links stance on this is due to security concerns.
Does Dlink own my router? Am I just leasing it? I'm at home, 5 miles from the nearest neighbor with only me here so security wise, logging into my router over the Ethernet cable is not a security issue.
This is another of the 32 character with upper/lower case, numbers and alpha, and special character password security-nazi things, I can only hope they grow out of before I lose my patience.