src/CI_Base_Model.php
public function created_at($row)
    {
        if (is_object($row))
        {
            $row->{$this->created_at_key} = date('Y-m-d H:i:s');
        }
        else
        {
            $row[$this->created_at_key] = date('Y-m-d H:i:s');
        }

        return $row;
    }
public function created_at($row)
    {
        if (is_object($row))
        {
            $row->{$this->created_at_key} = date('Y-m-d H:i:s');
        }
        else
        {
            $row[$this->created_at_key] = date('Y-m-d H:i:s');
        }

        return $row;
    }
MySQL DATETIME created_at and updated_at