foreach ($period as $day) {
//↓お届け希望日に表示させない日付を追加
if ($day->format('Y/m/d') == '2019/05/19' ||
    $day->format('Y/m/d') == '2019/05/20' ||
    $day->format('Y/m/d') == '2019/05/21') {
     continue;
    }
//ここまで

$deliveryDurations[$day->format('Y/m/d')] = $day->format('Y/m/d').'('.$dateFormatter->format($day).')';
}