> GPS fix+UTC time isn't sufficient to determine time zone

Most people understand that position alone can't determine time zones because their definitions change constantly. But surely with time + better positional accuracy we could do it? Nope.

Even with infinite precision in four dimensions, it's still a logical fallacy. Why? Because timezones are political definitions and many regions of the earth are contested (i.e. political control is ambiguous). So it is fundamentally impossible to determine time zone without identifying the political affiliation of the observer.