Follow the workflow below to troubleshoot this issue.
Verify that the information from the customer is accurate. In the AEC system, browse to System | Date & Time. If the time is not correct, click on the circular time sync button. Monitor the system to see if (or how quickly) the time is drifting.
Verify that the hardware is installed properly. Specifically, ensure that the system is not drawing too much power to operate properly. Perform your power calculations for the system to make sure it is within the acceptable range of power draw for the power supplies being used.
Verify that the diodes are installed properly. The back-biased suppression diodes are required at each and every device attached to an AEC output. It is important that these diodes are present for proper operation of the system. Improperly installed or missing diodes can damage the hardware. Consult the AEC Hardware Installation Manual for installation procedures.
If possible, setup the AEC with a 3rd party NTP time server. This can be located on your local network or a government time server. Consult the Software Manual for installation procedures.
If the prior steps still do not solve the issue, replace the CPU board. The timing circuit on that board may be defective and causing the time drift.