<?php
/**
* Fonction de conversion de date/heure du format américain (AAAA-MM-JJ HH:MM:SS) en Timestamp.
* @param string $datetime Date/heure au format américain (AAAA-MM-JJ HH:MM:SS)
* @return integer Timestamp en seconde
*/
function datetimeUS2Time($datetime)
{
  list($date, $time) = explode(' ', $datetime);
  list($hour, $minute, $second) = explode(':', $time);
  list($year, $month, $day) = explode('-', $date);
  $timestamp = mktime($hour, $minute, $second, $month, $day, $year);
  return $timestamp;
}
?>

<?php
echo datetimeUS2Time('1987-01-16 01:02:03'); // Affiche 537753723
?>