A Unix timestamp commonly counts seconds since 1970-01-01 00:00:00 UTC; some systems store milliseconds instead. A 10-digit modern value is often seconds and a 13-digit value often milliseconds, but check the source format rather than relying only on length.
Convert it with a timestamp converter, then display it in the viewer's time zone when that is the question. The instant stays the same while the local date and hour may change. If the result lands decades away from expectation, verify seconds versus milliseconds first.
Keep UTC and local representations labeled.
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