Backport commit 3d1c9a77c from Emacs

* lisp/org-timer.el (org-timer-show-remaining-time):
Don’t assume the remaining time is less than one hour.
Simplify.  The simplification removes the need for a
decode-time, and fixes a typo I introduced recently.

Fix org-timer-show-remaining-time > 1 hour
3d1c9a77c52664c8c3e4fa1ae25e1d13aab9b2f9
Paul Eggert
Sat Aug 17 17:22:25 2019 -0700

Note(km): This replaces porting of Emacs's c90a420779 (Add FIXMEs for
subsecond support, 2019-08-17).  It's modified to use
org-time-subtract and org-time-convert-to-integer for backward
compatibility.

lisp/org-timer.el

@@ -386,16 +386,15 @@ VALUE can be `on', `off', or `paused'."
 (defun org-timer-show-remaining-time ()
   "Display the remaining time before the timer ends."
   (interactive)
-  (require 'time)
-  (if (not org-timer-countdown-timer)
-      (message "No timer set")
-    (let* ((rtime (decode-time
-		   (time-subtract (timer--time org-timer-countdown-timer)
-				  (current-time))))
-	   (rsecs (nth 0 rtime))
-	   (rmins (nth 1 rtime)))
-      (message "%d minute(s) %d seconds left before next time out"
-	       rmins rsecs))))
+  (message
+   (if (not org-timer-countdown-timer)
+       "No timer set"
+     (format-seconds
+      "%m minute(s) %s seconds left before next time out"
+      ;; Note: Once our minimal require is Emacs 27, we can drop this
+      ;; org-time-convert-to-integer call.
+      (org-time-convert-to-integer
+       (org-time-subtract (timer--time org-timer-countdown-timer) nil))))))
 
 ;;;###autoload
 (defun org-timer-set-timer (&optional opt)