Use when scheduling across time zones or turning a local time into UTC without guessing DST. Input: to (IANA zones or KST, PST, CET...), optional from (zone of a local time, default UTC), time (ISO 8601, Unix seconds, or now). Output: JSON UTC instant, Unix time, and per zone: local ISO time with offset, weekday, abbreviation, DST and business-hours flags, day difference. Example: ?time=2026-10-12T09:00&from=Asia/Seoul&to=America/New_York,Europe/London

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