Diagnose "Network Time" checks the configured NTP.
Use your corporate Time Servers in the Time Server Configuration setting.
Usually the Domain Controller (Windows) is providing a NTP Time Server.
Various Time Servers are limited in request polling for each IP Adress (for example new request only after 5 minutes delay).
Please consider this to avoid errors.
Time drifts may happen, if the cpu load of the appliance or of the virtualization host is high for a long time.
To Monitor Time Drifts, it is possible to set the "Check time drift" Option and specify tolerance values for the actual test, and for the last hour.
If the time drift is more than specified in the tolerance, an error is reported.
Checking time fluctuations of last hour
Feb 16 01:32:01: 780 sec.
Feb 16 01:59:01: 3300 sec.
No Timeservers configured or outgoing UDP Pakets on Port 123 blocked, or request interval is too short.
Warning is caused if one of the NTP Servers fails, but the other is successful.
The following FAQ might be helpful: Synchronise the time in VMWare.