There are 3 options basically for NTP services start and stop
1) Start automatically if any ports are open, and stop when all ports are closed.
2) Start and stop with host.
3) Start and stop manually.
1)Start automatically if any ports are open, and stop when all ports are closed:
This one is the default settings which is recommended by the VMware. In this option if any ports are open the client attempts to contact the network resources of the services. Here point to be noted where if some ports are open, but the port for a particular services are closed, the attempt fails. It’s a drawback where the applicable outgoing port open then only the services begins to complete its usual task.
2) Start and stop with host:
The service starts shortly after the host starts and closes shortly before the host shuts down. Much like Start automatically if any ports are open, and stop when all ports are closed. This option means that the service regularly attempts to complete its tasks.
3) Start and stop manually:
When a user starts the NTP service, that service is kept running as long as the host is powered on. Here into this its not determined whether the port are open or not as this services is preserving the user-determined state.
So, at the conclusion option 1 is the best one to consider and also recommended by VMware.