When you upgrade vCenter from 6.7 to 7 version you might face this error:
Error Failed to set the time via NTP
Details failed to synch to the NTP server
Code com.vmware.applmgmt.err_ntp_sync_failed
Could not setup time synchronization.
Resolution Verify that provided NTP servers are valid
Solution would be to sincronize NTP service pointing internal/external IP but changing Time Syncronization Settings mode to host
Here it is more detailed article:
https://pradeeppapnai.wordpress.com/2019/06/02/vcentermigrationntperror/