Display postdate Spout Forms entries
Found the answer in the database. Apparently Sprout Forms uses the date field named "dateCreated". Also getting it in order by date (newest first) needs 'dateCreated desc'

{% for formEntry in craft.sproutForms.entries.formHandle('contact').order('dateCreated desc') %}
   {{ formEntry.dateCreated|date('d F Y') }}
{% endfor %}