Return a time zone string from a function

Question

Is this how I can return a time zone string from a function?

(defun timezone (ptz)
    "Gets the Posix Timezone String for major locations."

    (cond
     ((equal ptz "Alaska")
         "ASKT9AKDT,M3.2.0/2:00:00,M11.1.0/2:00:00")
     ((equal ptz "Denver-Colorado")
         "MST7MDT,M3.2.0/2:00:00,M11.1.0/2:00:00")
     ((equal ptz "Argentina")
         "ART3")
     ((equal ptz "Greenland")
         "WGST3WGT,M3.2.0/2:00:00,M11.1.0/2:00:00")))

Answer 1

This is absolutely the wrong thing to do. At no point should you ever use strings like "MST7MDT,M3.2.0/2:00:00,M11.1.0/2:00:00" to specify a timezone. Instead, take a standardized name like “America/Denver” and look it up in the time zone database. Emacs will even do that for you; just use the name whenever it wants a ZONE as an argument:

(format-time-string "%FT%T%z" nil "America/Denver")
⇒ "2022-12-05T22:57:51-0700"

(format-time-string "%FT%T%z" nil "Europe/London")
⇒ "2022-12-06T05:57:51+0000"