[PCI DSS 3.0] 10.4.2 Time data is protected.

10.4.2 Time data is protected.

10.4.2.a Examine system configurations and time- synchronization settings to verify that access to time data is restricted to only personnel with a business need to access time data.
10.4.2.b Examine system configurations, time synchronization settings and logs, and processes to verify that any changes to time settings on critical systems are logged, monitored, and reviewed.

Time synchronization technology is used to synchronize clocks on multiple systems. When clocks are not properly synchronized, it can be difficult, if not impossible, to compare log files from different systems and establish an exact sequence of event (crucial for forensic analysis in the event of a breach). For post-incident forensics teams, the accuracy and consistency of time across all systems and the time of each activity is critical in determining how the systems were compromised.