When setting my watch, anything within a minute is good enough. TOTP tokens are valid for a few minutes after Google Authenticator displays them. Meetings at work always start a minute or sometimes two after the hour. And when writing distributed software, systems other than cloud spanner (which rely on special hardware) must be built to tolerate clock differences of several minutes between systems.
So if we don’t ever rely on millisecond accurate time (without cesium and satellites being involved the worst case delta is still bad), why even attempt to achieve it? Why is NTP worth the complexity on most systems versus something like time protocol or course time?