Whether you submit detailed timesheets to clients or not, it’s a good
idea to estimate and keep track of the time you spend working on
tasks. I find that this helps me focus on the task at hand, and the
schedule feedback allows me to get a better idea of how much time it
will take to do something in the future. It’s also a good way to find
out where your time goes, of course.

It’s easy to clock work time under Org. When on a TODO item, type C-c
C-x C-i (org-clock-in). Work on the task. When you’re done, mark the task
as done with C-c C-t (org-todo), which automatically calls clock-out.
You can also clock out of a task manually by calling C-c C-x Co
(org-clock-out). The elapsed time will be added to the task headline. To
review the time summaries for your project, type C-c C-x C-d
(org-clock-display). If you want to add notes when you mark a task as
done, add “#+STARTUP: lognoteclock-out” to the beginning of your file.

How would you use this to keep track of your day? One way is to
keep track of the difference between your planned schedule and your
actual schedule. Add time estimates to your tasks. For example,

   ** TODO 20min Respond to mail

could represent twenty minutes of handling mail. Clock in and out of
tasks as you do them. To review the day’s accomplishments, type ‘l’
(org-agenda-log-mode) from the agenda view. This shows the completed
tasks and the time it took to accomplish them.

(Now I’m tempted to write an easy way to filter the Org task view by
estimated number of minutes. ;) Another nice little hack before that
would be to have a modeline countdown based on the estimate of the
currently-clocked-in task. Hmm. And then there’s displaying the list
of tasks for today and choosing which one to clock in on… That would
be fun to do, too. And then there’s calculating velocity and doing
evidence-based scheduling… The list goes on!)

Random Emacs symbol: minibuffer-local-map – Variable: Default keymap to use when reading from the minibuffer.