You can enter a date back to 30 days prior to filing if you so desire.
(c) Designation of certain exempt persons —(1) General. Except as provided in paragraph (c)(2) of this section, a bank must designate an exempt person by filing FinCEN Form 110. Such designation must occur by the close of the 30-calendar day period beginning after the day of the first reportable transaction in currency with that person sought to be exempted from reporting under the terms of this section
The opinions expressed here should not be construed to be those of my employer: PPDocs.com