The FBAR should be filed each year by the tax deadline of April 15th.

As stated on the IRS website, there is an automatic six-month extension granted to the filing deadline. Specific requests for this extension are not required.

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Please note that each (offshore) account must be listed on your FBAR, e.g. Solo401k trust, personal funds, IRA LLC, family trust, etc., that each account will need to be listed on the FBAR filing.

As reiterated by the Financial Crimes Enforcement Network (FinCen - those who are responsible for collection of the FBAR):

Accordingly, the due date for FBAR filings for foreign financial accounts maintained during calendar year 2017 is April 17, 2018, consistent with the Federal income tax due date. Filers who fail to file their 2017 calendar year FBAR by April 17, 2018, have an automatic extension up to October 15, 2018.

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There is an automatic 6-month extension for filing and the FBAR may be filed by October 15th. No specific request is needed to request an extension to file the FBAR.