Time synchronization feature will sync time accurate from NTP servers to your server. Once you choose the time zone, your server will get time based on the timezone you choose. But if you prefer to configure the time manually or to set time in an offline server (no internet connectivity to sync with NTP). In this case you have to disable automatic time synchronization ubuntu 18.04. inorder to set manually. For disabling the automatic time synchronization ubuntu, use the below method.
[email protected]:~$ timedatectl set-ntp no
Now you can manually set time and timezone as per your geo location.
Now set time manually using timedatectl command.
[email protected]:~$ timedatectl set-time 10:00