Do you synchronize the time for z/VSE ?
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Customers are increasingly implementing the Server Time Protocol (STP) to provide an accurate timestamp to operating systems.
z/VSE does not support STP. However, if the System z STP feature is installed you can configure a STP Coordinated Timing Network (CTN) which will then allow you to configure an NTP (Network Time Protocol) server to be used as the ETS (External Time Source). The SE (Service Element) on the CEC has an SNTP (Simple Network Time Protocol) client and it can access the NTP server on the HMC, if the HMC has been properly configured to enable it to become an NTP server.
The HMC when configured gets its NTP time from your "internal network" NTP server. Once the HMC is an NTP server it can be used to provide NTP time to the SE. STP code on the SE calculates the adjustment of time needed and STP code in the CEC itself steers the time so as to maintain time accuracy.
The STP Planning Guide on the Redbook web pages has some more information.
You don't need to read the whole book but going through Chapter 1 and then the External Time Source (ETS) section in Chapter 2 specific to NTP servers will give you good background. There are paragraphs related to z/VSE and z/VM.
It is currently being updated. The draft is here.
You may also be interested in the technical STP flash for operating systems that don't support STP.