Picking the right time system for the purpose is critical when you want to analyse very short periods. Sometimes it takes time to discover how to juggle with time.
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.
Background activities scheduled by third-party software currently use launchd, and run the risk of affecting the user. Would GCD be a better choice of dispatcher?
Schedule a periodic task as a Launch Agent. How close to the expected time does macOS actually run it?
Time should be universal, simple, and precise. Not in computers, though. Given enough clocks, it can behave oddly at times.
Time is central information for many functions on your Mac. This article explains the Network Time Protocol, and how it keeps time in OS X.