Как сохранить автоматически дату в формате timestamp на yii2?

public function behaviors()
    {
        return [
            'timestamp' => [
                'class' => TimestampBehavior::className(),
                'attributes' => [
                    ActiveRecord::EVENT_BEFORE_INSERT => 'created_at',
                    ActiveRecord::EVENT_BEFORE_UPDATE => 'updated_at'
                ],
                'value' => new Expression('NOW()')
            ],
        ];
?>

public function behaviors()
{
    return [
        [
            'class' => CorrectDateBehavior::class,
            'format' => 'datetime',
            'attributes' => [
                'dateFrom' => 'date_from',
                'dateTo' => 'date_to',
            ]
        ]
    ];
}

$model = new Post();
$model->date_from = 1524775512;
echo $model->dateFrom; // 26.4.2018 20:45:12

$model->dateFrom = '01.05.2018';
echo $model->date_from; // 1515110400