need assistance disabling Network Time Protocol (NTP)

[ginahoy]

When I first installed Linux, I changed the "Time and Date" GUI configuration setting to 'Manual' so theoretically there shouldn't be any ntp traffic, right? HOWEVER, surprisingly, 3 months later, my system clock is still within 1 second of 'official' time, which in my experience, is highly unlikely without ntp. I suspect the manual setting is either broken or overridden by another process or admin privileges. My objective is to eliminate ntp traffic.

Rather than troubleshooting the Time & Date GUI, I prefer to simply disable the ntp process. As a new Linux user, I searched for instructions and found this page. I skipped the first part (add restriction to ntp.config file) and instead attempted to disable the ntp daemon (nptd) and close port 123. However, I get errors because paths don't match my LM 18.2 Xfce install, and I'm hesitant to make changes I don't understand.

I would be grateful if someone would explain the steps to disable the ntp daemon and close port 123, assuming these are indeed the appropriate actions to eliminate ntp traffic. Thanks!