API page: https://api.drupal.org/api/drupal/modules%21node%21node.module/function/...
Currently, node_submit() only supports a pre-filled created date through the $node->date value. $node->date is only assigned for existing nodes in node_object_prepare().
If programmatically creating a node and manually setting the $node->created date, it would be helpful if node_submit() honored that for consistency.