org-agenda-start-day

org-agenda-start-day is a variable defined in `org-agenda.el'.
Its value is

nil

Documentation:
Start day for the agenda view.
Custom commands can set this variable in the options section.
This is usually a string like "2007-11-01", "+2d" or any other
input allowed when reading a date through the Org calendar.
See the docstring of `org-read-date' for details.