24 C.F.R. § 15.103
(b) Tolling the 20-day time period. Under the OPEN Government Act of 2007, HUD may toll the 20-day period:
(c) Extension of time periods for processing a request. In unusual circumstances, as defined in this paragraph, HUD may extend the time period for processing a FOIA request. In such circumstances, HUD will provide the requester with written notice setting forth the unusual circumstances for the extension and the date on which a determination is expected to be dispatched. This date will not exceed 10 working days beyond the general time limit established in paragraph (a) of this section. If processing a request would require more than 10 working days beyond the general time limit established in paragraph (a) of this section, HUD will offer the requester an opportunity to limit the scope of the request so that HUD may process it within the extra 10-day working period or arrange an alternative time period within which the FOIA request will be processed. For purposes of this section, unusual circumstances include:
(d) Aggregating multiple requests.
(1) HUD may aggregate multiple requests in cases where unusual circumstances exist and HUD determines that: