0:07:42sjl_I see it very well. Unfortunately that doesn't help.
0:07:56sjl_The issue seems to be that SBCL won't "notice" a timezone change until you restart it.
0:09:03sjl_e.g. run SBCL and run (decode-universal-time (get-universal-time)), note the time zone returned. In another window, sudo dpkg-reconfigure tzdata and change your time zone. Go back to SBCL and eval the form again, and the timezone will not have changed. Exit SBCL, run it again, and eval the form again, and *now* you get the new timezone.
0:09:17sjl_Digging though the SBCL code to see where it's getting cached now...
0:55:24sjl_Figured it out. SBCL's uses localtime_r when it computes the time zone used by decode-universal-time. localtime_r doesn't have to reset the tzdata like localtime does, according to man 3 localtime.