It is good for 12 months.
Per instructions:
e. Law Enforcement Certification. Item 17 must be completed for an
individual transferee, unless the transferee is licensed as a manufacturer,
importer, or dealer under the GCA and is a special (occupational) taxpayer
under the NFA at the time of the submission of the application for transfer.
The chief law enforcement officer is considered to be the Chief of Police for
the transferee's city or town of residence; the Sheriff for the transferee's
county of residence; the Head of the State Police for the transferee's State of
residence; a State or local district attorney or prosecutor having jurisdiction
inthe transferee's area of residence; or another person whose certification is
acceptable to the Director, Bureau of Alcohol, Tobacco, Firearms and
Explosives. If someone has specific delegated authority to sign on behalf of
the Chief of Police, Sheriff, etc., this fact must be noted by printing the
Chief's, Sheriff's, or other authorized official's name and title, followed by the
word "by" and the full signature and title of the delegated person. The
certificate must be dated no more than one year prior to the date of receipt of
the application.