systemd-timedated is a system service that may be used as mechanism to change the system clock and timezone, as well as to enable/disable NTP time synchronization. systemd-timedated is automatically activated on request and terminates itself when it is unused.
The tool timedatectl(1) is a command line client to this service.
See the developer documentation  for information about the APIs systemd-timedated provides.
systemd(1), timedatectl(1), localtime(5), hwclock(8)