The QRDA III documentation states that all or no time zones should exist when exporting for attestation.

In the case where an EHR provides time zones and another does not provide a timezone the most logical reasoning to allow providers to define a timezone for their QRDA I import. In this case, time zones would be be calculated using offsets and the patient files would all be designated using a single time zone. Problematically, if a QRDA I comes in without a timezone there is no guaranteed way to account for daylight savings time. 

For instance, if provider must assign a static timezone because an EHR did not provide that time zone in a QRDA I export, all date times associated to a patient files during day light savings time between 11:00pm and 11:59pm would calculate into the next day reducing accuracy for those specific values. 

What is CMS recommendation?