The NTP (Network Time Protocol) is an Internet protocol that is used to synchronize the time on your system with a centralized Network Time Protocol server. It also analyses the timestamp values including the frequency of errors and the stability.
See the instructions for setting up time zone and NTP specifically of Debian, Ubuntu OS below.

1. Configure the system clock in Ubuntu & Debian servers.

# timedatectl

2. Display the current time and date.

# timedatectl

3. Display all available Time zones.

# timedatectl list-timezones

4. Display a particular Time zone under Asia starting with the alphabet H.

# timedatectl list-timezones | grep  -o "Asia/H.*"

5. To change or set a Time zone you can use the below command. E.g. Change to Hong Kong.

# timedatectl set-timezone Asia/Hong_Kong

6. To enable NTP to synchronize time with Internet time.

# timedatectl set-ntp on