This process requires a user with a special authority * IOSYSCFG.
Configuring the AS400 to connect to the NTP Server can be done using the CHGNTPA (Change SNTP Attribute) command.

Some things to be aware of:
- Remote System: NTP Server Address that will be used (maximum 3 NTP Servers)
- Client Autostart: * YES if you want to automate this service when the STRTCPSVR command is used (if AS400 is the client)
- Client poll interval: Parameter to determine the interval AS400 will connect to the NTP Server
- Client Minimum, Maximum Adjustment: Parameter Minimum and Maximum time for AS400 to make time corrections
- Client Adjustment Threshold: Parameters to determine whether AS400 will make time settings or adjustments.
- Client Activity Log: Parameters to enable or disable SNTP Logger
- Client Autostart: * YES if you want to automate this service when the STRTCPSVR command is used (if AS400 is the server)
- Service Activity Log: The type of activity the log will log
- Synchronization Required: System synchronization if AS400 as NTP Server and NTP Client
Any changes to the NTP Attribute will be effective by restarting the NTP Service. Using the ENDTCPSVR SERVER (* NTP) and STRTCPSVR SERVER (* NTP) commands.
Notes:
For this setting, pay attention to the behavior of the applications used on the AS400. Is the time change a concern for the application or not.
For example: AS400 which is used every day, there is a downtime for 5 minutes for the end of the day processing. This time is suitable for adjusting / setting the AS400 with NTP time. So I made the Poll interval setting for 1440 min and submitted it during the downtime.