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Comment by thrdbndndn | Hacker News Reader

I probably should read into details, but I don't get it from the summary at least.

How would future time zone change or DST change affect it at all? Is it about your pre-defined time would no longer be aligned with a nice "local time" like 0:00?

Because things would still happen at the exactly same "moment" (absolute time or time delta from now) in UTC regardless any TZ change isn't it?

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Doesn't help you much if you stored an UTC for a future meeting, then the TZ rules change, and then you show up an hour late.

True, although if your meeting will be attended by people in multiple time zones, you need to declare the time in some absolute sense anyway.

The difference is something like storing your comment was made at 2022-03-13+10:40. Which the time zone has been set and will always be the same at as it's in the past vs "set an alarm for 2023-03-13+6:00" I want the to happen at 6:00am whether or not my country continues to observe day light saving time.

You have a timestamp in the future for example the time when a session at a conference starts. If to want to store this as UTC you will have to convert it from the local timezone of the conference location. You can always go back from the UTC timestamp to the local timestamp by performing the reverse conversion EXCEPT if the conversion involves daylight savings and the rule changes between now and the event in the future. While rare, daylight savings rules sometimes do change. I guess even local timezone offsets might change once in a while. When this happens the conversion back from UTC to the local time will be wrong unless you keep track of more than the UTC timestamp.

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