Field type date bad formatting
Datetime values in storage are UTC, if you are storing datetime values by your own, you have to pay attention on this and display datetimes to users considering your timezone ('Pacific/Noumea' probably declared in your php.ini or user's timezone present in user profile).

Storing 2018-05-02T08:23:25 as your current datetime in caledonia in database is a nonsense considering timezone, because the format DateTimeItemInterface::DATETIME_STORAGE_FORMAT do not include timezone.

$date = strtotime($node-&gt;field_paiement_date-&gt;value);
\Drupal::service('date.formatter')
  -&gt;format($date, 'custom', 'Y-m-d H:i:s', drupal_get_user_timezone());
\Drupal::service('date.formatter')
  -&gt;format($date, 'custom', 'Y-m-d H:i:s', 'Pacific/Noumea');