How to implement a mysql date or datetime field correctly in hook_schema()?
You should provide a fallback type (varchar) for the case that the database is not mysql.

'pubblish_date' =&gt; array(
  'description' =&gt; t('The pubblish date for the single news'),
  'type' =&gt; 'varchar',
  'mysql_type' =&gt; 'datetime',
  'not null' =&gt; FALSE,
),
'unpublish_date' =&gt; array(
  'description' =&gt; t('The unpublish date for the single news'),
  'type' =&gt; 'varchar',
  'mysql_type' =&gt; 'datetime',
  'not null' =&gt; FALSE,
),


However, the messages you see come from the Schema module. This problem is already recorded as issue #468644.

The implementation of the mysql datetime in your schema is fine. You can safely ignore these messages.  I would say that these "advice messages" are caused by a bug in the Schema module.