I am trying to search for specific matrix blocks by date like so:
$criteria = craft()->elements->getCriteria(ElementType::MatrixBlock);
$criteria->ownerId = $entry->id;
$criteria->type = 'myMatrixBlockType';
$criteria->myMatrixBlockDateField = "2016-06-01 04:00:00";
$criteria->limit = 10;
$blocks = $criteria->find();
It seems that no matter what format the date is, all blocks from the matrix field in the entry are returned. Any help is appreciated!