If you’re anything like me, your task list is long and growing, but
the time you have is just as fixed. How do you manage that? I handle
that problem by looking at my calendar and my task list together when
I’m planning my day. I tend to be too optimistic about my tasks,
trying to schedule more into my day than I should. Fortunately, Emacs
can help me make sure I don’t overcommit. Here’s how it works.

When I create and schedule tasks, I try my best to add time estimates.
The numbers in the TODO headline represent minutes.

* TODO 15 Announce tea party
  SCHEDULED: <2007-12-08 Sat>
* DONE 30 Drop letters off at post office
  SCHEDULED: <2007-12-08 Sat>
* TODO 60 Write blog post about tasks
  SCHEDULED: <2007-12-08 Sat>
* TODO 60 Make book notes
  SCHEDULED: <2007-12-09 Sun>
* TODO 30 Start on my letter for 2007
  SCHEDULED: <2007-12-08 Sat>
* TODO 60 Follow up with DemoCamp contacts
  SCHEDULED: <2007-12-08 Sat>
  DEADLINE: <2007-12-09 Sun>
* TODO 60 Respond to mail
  SCHEDULED: <2007-12-08 Sat>

Then my custom agenda view looks like this:

Day-agenda:
Saturday   8 December 2007
  6:00......  --------------------
  8:00......  --------------------
 10:00......  --------------------
 12:00......  --------------------
 14:00......  --------------------
 14:00-17:15  Scheduled:  TODO Take another driving lesson - emergency stuff
 16:00......  --------------------
 18:00......  --------------------
 20:00......  --------------------
 22:00......  --------------------
              In   1 d.:  TODO 60 Follow up with DemoCamp contacts
              Scheduled:  TODO 15 Announce tea party
              Scheduled:  TODO 60 Write blog post about tasks
              Scheduled:  TODO 30 Start on my letter for 2007
              Scheduled:  TODO 60 Follow up with DemoCamp contacts
              Scheduled:  TODO 60 Respond to mail
              In 937 d.:  101 things in 1001 days
62.7% load: 225 minutes to be scheduled, 359 minutes free, 134 minutes gap

I’ll need to figure out over the next few weeks what kind of a load
threshold is good (you really don’t want to try for 100%), but at
least it’s visible!

(setq org-agenda-custom-commands
      '(("i" "My agenda"
         ((org-agenda-list nil nil 1)
          (sacha/org-load)))
        ;; ... other stuff goes here
      ))

(defun sacha/org-show-load ()
  "Show my unscheduled time and free time for the day."
  (interactive)
  (let ((time (sacha/org-calculate-free-time
               ;; today
               (calendar-gregorian-from-absolute (time-to-days (current-time)))
               ;; now
               (let* ((now (decode-time))
                      (cur-hour (nth 2 now))
                      (cur-min (nth 1 now)))
                 (+ (* cur-hour 60) cur-min))
               ;; until the last time in my time grid
               (let ((last (car (last (elt org-agenda-time-grid 2)))))
                 (+ (* (/ last 100) 60) (% last 100))))))
    (message "%.1f%% load: %d minutes to be scheduled, %d minutes free, %d minutes gap"
            (/ (car time) (* .01 (cdr time)))
            (car time)
            (cdr time)
            (- (cdr time) (car time)))))

(defun sacha/org-load (match)
  "Can be included in `org-agenda-custom-commands'."
  (let ((inhibit-read-only t)
        (time (sacha/org-calculate-free-time
               ;; today
               (calendar-gregorian-from-absolute org-starting-day)
               ;; now if today, else start of day
               (if (= org-starting-day
                      (time-to-days (current-time)))
                   (let* ((now (decode-time))
                          (cur-hour (nth 2 now))
                          (cur-min (nth 1 now)))
                     (+ (* cur-hour 60) cur-min))
                 (let ((start (car (elt org-agenda-time-grid 2))))
                   (+ (* (/ start 100) 60) (% start 100))))
                 ;; until the last time in my time grid
               (let ((last (car (last (elt org-agenda-time-grid 2)))))
                 (+ (* (/ last 100) 60) (% last 100))))))
    (goto-char (point-max))
    (insert (format
             "%.1f%% load: %d minutes to be scheduled, %d minutes free, %d minutes gap"
             (/ (car time) (* .01 (cdr time)))
             (car time)
             (cdr time)
             (- (cdr time) (car time))))))

(defun sacha/org-calculate-free-time (date start-time end-of-day)
  "Return a cons cell of the form (TASK-TIME . FREE-TIME) for DATE, given START-TIME and END-OF-DAY.
DATE is a list of the form (MONTH DAY YEAR).
START-TIME and END-OF-DAY are the number of minutes past midnight."
  (save-window-excursion
  (let ((files org-agenda-files)
        (total-unscheduled 0)
        (total-gap 0)
        file
        rtn
        rtnall
        entry
        (last-timestamp start-time)
        scheduled-entries)
    (while (setq file (car files))
      (catch 'nextfile
        (org-check-agenda-file file)
        (setq rtn (org-agenda-get-day-entries file date :scheduled :timestamp))
        (setq rtnall (append rtnall rtn)))
      (setq files (cdr files)))
    ;; For each item on the list
    (while (setq entry (car rtnall))
      (let ((time (get-text-property 1 'time entry)))
        (cond
         ((and time (string-match "\\([^-]+\\)-\\([^-]+\\)" time))
          (setq scheduled-entries (cons (cons
                                         (save-match-data (appt-convert-time (match-string 1 time)))
                                         (save-match-data (appt-convert-time (match-string 2 time))))
                                        scheduled-entries)))
         ((and time
               (string-match "\\([^-]+\\)\\.+" time)
               (string-match "^[A-Z]+ \\([0-9]+\\)" (get-text-property 1 'txt entry)))
          (setq scheduled-entries
                (let ((start (and (string-match "\\([^-]+\\)\\.+" time)
                                 (appt-convert-time (match-string 1 time)))))
                  (cons (cons start
                              (and (string-match "^[A-Z]+ \\([0-9]+\\)" (get-text-property 1 'txt entry))
                                   (+ start (string-to-number (match-string 1 (get-text-property 1 'txt entry))))))
                        scheduled-entries))))
         ((string-match "^[A-Z]+ \\([0-9]+\\)" (get-text-property 1 'txt entry))
          (setq total-unscheduled (+ (string-to-number
                                      (match-string 1 (get-text-property 1 'txt entry)))
                                     total-unscheduled)))))
      (setq rtnall (cdr rtnall)))
    ;; Sort the scheduled entries by time
    (setq scheduled-entries (sort scheduled-entries (lambda (a b) (< (car a) (car b)))))

    (while scheduled-entries
      (let ((start (car (car scheduled-entries)))
            (end (cdr (car scheduled-entries))))
      (cond
       ;; are we in the middle of this timeslot?
       ((and (>= last-timestamp start)
             (<= last-timestamp end))
        ;; move timestamp later, no change to time
        (setq last-timestamp end))
       ;; are we completely before this timeslot?
       ((< last-timestamp start)
        ;; add gap to total, skip to the end
        (setq total-gap (+ (- start last-timestamp) total-gap))
        (setq last-timestamp end)))
      (setq scheduled-entries (cdr scheduled-entries))))
    (if (< last-timestamp end-of-day)
        (setq total-gap (+ (- end-of-day last-timestamp) total-gap)))
    (cons total-unscheduled total-gap))))

Random Emacs symbol: select-safe-coding-system-function – Variable: Function to call to select safe coding system for encoding a text.