If your "epoch" source is Windows (Active directory, for instance), you need to be aware that there is a difference of 11644473600, when you compare a Unix epoch to a Windows epoch (Unix timestamp is smaller).
See http://www.powershelladmin.com/wiki/Convert_windows_nanosecond_epoch_timestamp_to_human-readable_date_and_vice_versa#Perl_Source_Code.
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