In the system configuration file, how do I set the
   TIMEZONE option for Eastern daylight time. I have tried
   setting to an offset of 300 minutes from GMT but the
   system always shows PDT instead of EDT. While I'm sure
   the theory is quite simple, I am at a loss as to how it
   works.

You need to either set your `TZ' environment variable (to, e.g.,
`EST5EDT'), or make a symlink from one of the files in
/usr/share/zoneinfo to /etc/localtime.