Google Drive上の指定したフォルダにあるフォームの一定期間過ぎた回答を削除するGASコード

function DeleteOldResponses() {
  let id = "1234567890_abcdefghijklmnopqrstuvwxzy";
  let folder = DriveApp.getFolderById(id);
  let files = folder.getFiles();
  let currentTime = new Date().valueOf(); //今日の日付 Today’s Date 
  let expirationTime = currentTime - 90*24*3600*1000;
  //必要に応じて変更。この例では、90は保管日数。24*3600*1000 は1000分の1秒単位で1日。
  //Change to suit your needs. In this example, 90 is the number of days elapsed. 24*3600*1000 is one day in milliseconds.
  while (files.hasNext()) {
    let file = files.next();
    let mimeType = file.getMimeType();
    //Googleフォームだけを抽出して処理 Extract and process only Google Forms.
    if (mimeType == 'application/vnd.google-apps.form') {
      let id2 = file.getId();
      let form = FormApp.openById(id2);
      let formResponses = form.getResponses();
      for (let i = 0; i < formResponses.length; i++) {
        let formResponse = formResponses[i];
        let responseTime = formResponse.getTimestamp().valueOf();
        if (responseTime < expirationTime) {
          let id3 = formResponse.getId();
          form.deleteResponse(id3);
        }
      }
    }
  }
}