Often it’s whenever someone “official” witnesses it for the record. When my mom recently died of cancer, she was gone (and slightly cool to the touch), when my dad woke up at 7 am. So we know it was sometime before that. But then we had to call the hospice worker (she was doing hospice at home) and their medical staff came and made the official call. So her time of death is listed at around 8:30 am that day. All we really know it was sometime between 3 & 7 am.
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