org-time-clocksum-use-effort-durations

org-time-clocksum-use-effort-durations is a variable defined in `org.el'.
Its value is

nil

Documentation:
When non-nil, M-x org-clock-display uses effort durations.
E.g. by default, one day is considered to be a 8 hours effort,
so a task that has been clocked for 16 hours will be displayed
as during 2 days in the clock display or in the clocktable.

See `org-effort-durations' on how to set effort durations
and `org-time-clocksum-format' for more on time clock formats.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.4 of Emacs.