If you write a collection agency a dispute/verify letter and don't specify 30 days is there any law that states they can take longer or are they bound to the 30 day rule?

Here is how the Fair Credit Reporting Act reads:

§ 611. Procedure in case of disputed accuracy [15 U.S.C. § 1681i]

(a) Reinvestigations of Disputed Information

(1) Reinvestigation Required

(A) In general. Subject to subsection (f), if the completeness or accuracy of any
Item of information contained in a consumer's file at a consumer reporting
Agency is disputed by the consumer and the consumer notifies the agency
Directly, or indirectly through a reseller, of such dispute, the agency shall,
Free of charge, conduct a reasonable reinvestigation to determine whether
The disputed information is inaccurate and record the current status of the
Disputed information, or delete the item from the file in accordance with
Paragraph (5), before the end of the 30-day period beginning on the date on
which the agency receives the notice of the dispute from the consumer or
reseller.

(B) Extension of period to reinvestigate. Except as provided in subparagraph
(C), the 30-day period described in subparagraph (A) may be extended for
Not more than 15 additional days if the consumer reporting agency receives
Information from the consumer during that 30-day period that is relevant to
The reinvestigation.

(C) Limitations on extension of period to reinvestigate. Subparagraph (B) shall
Not apply to any reinvestigation in which, during the 30-day period
July 30, 2004 47
Described in subparagraph (A), the information that is the subject of the
Reinvestigation is found to be inaccurate or incomplete or the consumer
Reporting agency determines that the information cannot be verified.