Less latency in org-timer-item.

* org-timer.el (org-timer-item): Refactoring. Compute timer string
  before inserting it in the buffer
* org-timer.el (org-timer): added an optional argument to return timer
  string instead of inserting it.

lisp/org-timer.el

@@ -145,18 +145,23 @@ With prefix arg STOP, stop it entirely."
   (org-timer-set-mode-line 'off))
 
 ;;;###autoload
-(defun org-timer (&optional restart)
+(defun org-timer (&optional restart no-insert-p)
   "Insert a H:MM:SS string from the timer into the buffer.
 The first time this command is used, the timer is started.  When used with
 a \\[universal-argument] prefix, force restarting the timer.
 When used with a double prefix argument \
 \\[universal-argument] \\universal-argument], change all the timer string
 in the region by a fixed amount.  This can be used to recalibrate a timer
-that was not started at the correct moment."
+that was not started at the correct moment.
+
+If NO-INSERT-P is non-nil, return the string instead of inserting
+it in the buffer."
   (interactive "P")
-  (if (equal restart '(4)) (org-timer-start))
-  (or org-timer-start-time (org-timer-start))
-  (insert (org-timer-value-string)))
+  (when (or (equal restart '(4)) (not org-timer-start-time))
+    (org-timer-start))
+  (if no-insert-p
+      (org-timer-value-string)
+    (insert (org-timer-value-string))))
 
 (defun org-timer-value-string ()
   (format org-timer-format (org-timer-secs-to-hms (floor (org-timer-seconds)))))
@@ -196,23 +201,21 @@ that was not started at the correct moment."
   "Insert a description-type item with the current timer value."
   (interactive "P")
   (cond
-   ;; If we are in a timer list, insert item like `org-insert-item'.
+   ;; In a timer list, insert with `org-insert-item-internal'.
    ((and (org-in-item-p)
 	 (save-excursion
 	   (org-beginning-of-item)
 	   (looking-at "[ \t]*[-+*][ \t]+[0-9]+:[0-9]+:[0-9]+ ::")))
-    (org-insert-item-internal (point))
-    (org-timer (if arg '(4)))
-    (insert ":: "))
-   ;; We are still are in a list, of a wrong type: throw an error.
+    (org-insert-item-internal (point) nil (concat (org-timer (when arg '(4)) t) ":: ")))
+   ;; In a list of another type, don't break anything: throw an error.
    ((org-in-item-p)
     (error "This is not a timer list"))
-   ;; Else, go to beginning of line, and insert the timer
+   ;; Else, insert the timer correctly indented at bol.
    (t
     (beginning-of-line)
     (org-indent-line-function)
     (insert  "- ")
-    (org-timer (if arg '(4)))
+    (org-timer (when arg '(4)))
     (insert ":: "))))
 
 (defun org-timer-fix-incomplete (hms)