Emacs comes with a few thousand lines of code for calendar calculations. Surely timezone calculations must be a properly solved problem as well! At least, that’s what one would expect given the existence of the very handy M-x display-time-world. Except, it’s not:
(defun display-time-world-display (alist) "Replace current buffer text with times in various zones, based on ALIST." (let ((inhibit-read-only t) (buffer-undo-list t) (old-tz (getenv "TZ")) (max-width 0) result fmt) (erase-buffer) (unwind-protect (dolist (zone alist) (let* ((label (cadr zone)) (width (string-width label))) (setenv "TZ" (car zone)) (push (cons label (format-time-string display-time-world-time-format)) result) (when (> width max-width) (setq max-width width)))) (setenv "TZ" old-tz)) (setq fmt (concat "%-" (int-to-string max-width) "s %s\n")) (dolist (timedata (nreverse result)) (insert (format fmt (car timedata) (cdr timedata)))) (delete-char -1)))
edit: Looks like this got fixed properly!