There is the Internet NTP [Network Time Protocol] or even the SNTP [Simple Network Time Protocol]. They have been implemented for a number of operating systems, but I'm not sure whether for Mac systems. Clock synchronization to well within a millisecond is normal.
BTW, the "father" of NTP is something of an aviation buff - keeping track of even which runway his airliner uses at each airport. His eyesight is too poor to drive, much less be a pilot. He's located at the Univ of Delaware, USA. IIRC the NTP document is Internet RFC 1305. There is an active newsgroup.
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