-(defun org-timer-set-timer (minutes)
- "Set a timer."
- (interactive "sTime out in (min)? ")
- (if (not (string-match "[0-9]+" minutes))
- (org-timer-show-remaining-time)
+(defun org-timer-set-timer (&optional opt)
+ "Prompt for a duration and set a timer.
+
+If `org-timer-default-timer' is not zero, suggest this value as
+the default duration for the timer. If a timer is already set,
+prompt the user if she wants to replace it.
+
+Called with a numeric prefix argument, use this numeric value as
+the duration of the timer.
+
+Called with a `C-u' prefix arguments, use `org-timer-default-timer'
+without prompting the user for a duration.
+
+With two `C-u' prefix arguments, use `org-timer-default-timer'
+without prompting the user for a duration and automatically
+replace any running timer."
+ (interactive "P")
+ (let ((minutes (or (and (numberp opt) (number-to-string opt))
+ (and (listp opt) (not (null opt))
+ (number-to-string org-timer-default-timer))
+ (read-from-minibuffer
+ "How many minutes left? "
+ (if (not (eq org-timer-default-timer 0))
+ (number-to-string org-timer-default-timer))))))
+ (if (not (string-match "[0-9]+" minutes))
+ (org-timer-show-remaining-time)