15 C.F.R. § 90.6

When a challenge may be filed.

(a) A request for a challenge to a population estimate may be filed any time up to 90 days after the release of the estimate by the Census Bureau. Publication by the Census Bureau on its website ( www.census.gov ) shall constitute release. Documentation requesting a challenge of any estimate may also be filed any time up to 90 days after the date the Census Bureau, on its own initiative, revises that estimate.

(b) If, however, a governmental unit has a sufficiently meritorious reason for not filing in a timely manner, the Census Bureau has the discretion to accept the late request.