PHP function to turn a DateTime object to Delphi's TDate type. Delphi's TDate type is something like UnixTimestamp; it is a (float) number but it has as a starting poing the 1899-12-30 instead of the 1970-01-01 as is the case in the UnixTimestamp.

php2delphiTDate.php

<?php
/**
 * For the sake of example, I assume that the caller only needs the date without any time information.
 * If you also need the time, you will have to modify the following code a little.
 * @param object $phpDate
 * A DateTime PHP object
 * @return int
 * The number of days from 1899-12-30 (Delphi's starting point). This is also the correct value to be
 * stored as a TDate type variable in Delphi.
 */
function php2delphiTDate(DateTime $phpDate) {
  // The difference between UnixTimestamp's starting point and DelphiTDate's starting point.
  $UnixDelphiDiff = 25569;
  // Create a DateTime object based on the starting point of the Unix Timestamp.
  $unixDate = date_create_from_format('d/m/Y H:i:s', '01/01/1970 00:00:00');
  // Get the difference in a DateInterval object.
  $interval = $phpDate->diff($unixDate);
  // Sum the days of the difference with the days of the difference between
  // UnixTimestamp first date and Delphi's first date.
  return $interval->days + $UnixDelphiDiff;
}