CMS posted their instructions along with the compliance dates last Friday (May 11). That posting can be found at the following URL.
http://www.cms.hhs.gov/transmittals/downloads/R1240CP.pdf
I have extracted the information related to dates of compliance for your convenience. It should be noted that use of the K3 segment in the ANSI 837 format as indicated earlier remains unchanged from previous announcements.
Effective for acute care inpatient PPS discharges on or after October 1, 2008, the Secretary cannot assign cases with these conditions to a higher paying DRG unless they were present on admission. This instruction will require hospitals to begin reporting the POA code on claims with discharges beginning on or after October 1, 2007. Although hospitals must report the POA code on the claim, the information will not be used by claims processing systems until January 1, 2008. Beginning with claims with discharges on or after January 1, 2008, if hospitals do not report a valid POA code for each diagnosis on the claim, the claim will continue to process. However, hospitals will be provided with a remark code on their remittance advice advising them that they did not correctly submit the POA code on the claim. Beginning April 1, 2008, if hospitals do not report a valid POA code for each diagnosis on the claim, the claim will be returned to the hospital for correct submission of POA information.