<?php

class Meanbee_ShoppingAssistant_Model_Resource_Request extends Mage_Core_Model_Resource_Db_Abstract
{
    public function _construct()
    {
        $this->_init("meanbee_shoppingassistant/request", "entity_id");
    }
}

<?php

class Meanbee_ShoppingAssistant_Model_Resource_Request extends Mage_Core_Model_Resource_Db_Abstract
{
    public function _construct()
    {
        $this->_init("meanbee_shoppingassistant/request", "entity_id");
    }

    protected function _prepareDataForSave(Mage_Core_Model_Abstract $object)
    {
        if ((!$object->getId() || $object->isObjectNew()) && !$object->getCreatedAt()) {
            $object->setCreatedAt($this->formatDate(true));
        }
        return parent::_prepareDataForSave($object);
    }

}

Set a created_at date before saving a new request
Set a created_at date before saving a new request
