How to save multi date and time in node programmatically?
If converting the two is your problem following may help you

foreach ($form_state['values']['field_event_date']['und'] as $key=&gt; $value) {
  $node-&gt;field_event_date['und'][$key]['value'] = strtotime($form_state['values']['field_event_date']['und'][$key]['value']['date'] . ' ' . $form_state['values']['field_event_date']['und'][$key]['value']['time'])
}


strtotime() should be good enough.

I am assuming you are doing node_save() some where.