An internal NTP server that provides time services to the Cardholder Data Environment is?

According to the PCI DSS v3.2.1 Quick Reference Guide1, an internal NTP server that provides time services to the cardholder data environment is in scope for PCI DSS if it stores processes or transmits cardholder data, regardless of whether it provides authentication services to systems in the DMZ or not. This is one of the requirements for preventing unauthorized access to cardholder data using time services.