[roywiggins]

That sort of assumes there's one time zone that's being used per spacetime coordinate, which isn't guaranteed. You can get political situations where de facto and de jure time diverge, or where different authorities nominally in charge of the time in a place disagree.

Lebanon seems to have experienced exactly this recently:

https://www.bbc.com/news/world-middle-east-65079574

It does unambiguously give you a spacetime coordinate (useful) but it doesn't unambiguously tell you what local time you should use for an occurrence, and the answer would really depend on who was asking.