Create a content node from another content
If both your content types are defined for Plannning and Appointment already, you can easily create appoint nodes on-the-fly when a Planning node is saved.

You want to look at the following 2 references:


hook_node_insert()
Programmatically create nodes


It would look something like this (NOT TESTED):

function mymodule_node_insert($node) {
  if ($node-&gt;type == 'planning') {
    foreach (element_children($node-&gt;field_appointment_dates) as $a_single_appointment_date) {
      $appt_node = new stdClass();
      $appt_node-&gt;type = 'appointment';
      node_object_prepare($appt_node);
      $appt_node-&gt;language = LANGUAGE_NONE; // Or your language type ...
      $appt_node-&gt;title = 'Some new appointment';
      $appt_node-&gt;field_appointment_date = $a_single_appointment_date[0]['value'];
      node_save($appt_node);
    }
  }
}