How do I set the creation time of a node during a migration using the Migrate module?
I've been using prepareRow in my class to solve this kind of problem .

First of all I add a new Source Field to the MigrateSourceSQL

$source_fields = array(
  'created' =&gt; t('the created date'),


then in prepareRow I added the php for the timestamp and attached it to the row.  

$row-&gt;changed = $nowtimestamp;


And then assign with addFieldMapping

$this-&gt;addFieldMapping('field_created_date', 'changed' );


This seems to work fine for me.