variant_date_to_timestamp() assumes the COM date in the current Windows time zone and converts it to the current PHP time zone(PHP 5, PHP 7, PHP 8)
variant_date_to_timestamp — Converts a variant date/time value to Unix timestamp
   Converts variant from a VT_DATE
   (or similar) value into a Unix timestamp.  This allows easier
   interopability between the Unix-ish parts of PHP and COM.
  
variantThe variant.
   Returns a unix timestamp, or null on failure.
  
variant_date_to_timestamp() assumes the COM date in the current Windows time zone and converts it to the current PHP time zone