Early Macs normally had their clocks synced manually, until System 8.5 introduced support for NTP. That later switched to a proprietary service, timed, in macOS 10.13 High Sierra.
timed
How to ensure your Mac’s clock and time is as accurate as possible, what can cause problems, and how it works using the timed daemon, as revealed in the log.
It’s surprising that macOS can be slower to fully register the annual ‘spring forward’ change than you are walking round manually changing your clocks.
When you find one, bugs will necessarily be multiple. If you think you’ve found one, you can be fairly confident that you’ll find more. Four bugs in macOS for the price of one.
Changes include frequent timechecks by timed, harder access to info about keychains, a couple of possible AppleScript bugs, and APFS snapshots.
High Sierra has done away with the ntpd daemon for keeping your Mac’s clock in sync with a standard time server. This now works as in iOS, using the timed daemon.
The Eclectic Light Company 