A Google Apps standalone script which automatically creates a new diary entry with a prefilled header, and clears out old, unfilled entries.

autodiary.standalone.apps.js

// To install, copy script over to new project at scripts.google.com.
// Create two folders, Diary and Archive (one may be inside the other).
// Configure the constants below (you can find the folder IDs in your address bar at drive.google.com)
// Create a new time-driven trigger set to Day timer (Resources > Current project's triggers > Add a new trigger)

// For diary entries
var DIARY_FOLDER_ID = '<configure me>';
// For empty diary entries cleaned out. 
// Note: they're not deleted, due to concern of runaway deletion with no backup
var DIARY_ARCHIVE_FOLDER_ID = '<configure me>';

function dailyCron() {
  clearEmptyEntries();
  createDiaryEntry();
}

function clearEmptyEntries() {
  var diaryFolder = DriveApp.getFolderById(DIARY_FOLDER_ID);
  var archiveFolder = DriveApp.getFolderById(DIARY_ARCHIVE_FOLDER_ID)
  
  var entries = diaryFolder.getFiles();
  while (entries.hasNext()) {
    var file = entries.next();
    if (_isEntryEmpty(file)) {
      Logger.log('Archiving empty entry %s (%s)', file.getName(), file.getId());
      _moveFile(file, diaryFolder, archiveFolder);
    }
  }
}

function _isEntryEmpty(file) {
  // An entry is considered empty if its last update 
  // was within 1 second of its creation time.
  var delta_ms = file.getLastUpdated() - file.getDateCreated();
  return delta_ms <= 1000;
}

function createDiaryEntry() {
  var date = new Date;
  var doc = _createDiaryEntry(date);
  _fillDiaryEntry(doc, date);
  Logger.log('Created new diary entry %s (%s)', doc.getName(), doc.getId());
  return doc;
}

function _createDiaryEntry(date) {
  var title = _formatDate(date);
  var doc = DocumentApp.create(title);
  var file = DriveApp.getFileById(doc.getId());
  _moveFile(file, 
            DriveApp.getRootFolder(),
            DriveApp.getFolderById(DIARY_FOLDER_ID));
  return doc;
}

function _moveFile(file, sourceFolder, destFolder) {
  destFolder.addFile(file);
  sourceFolder.removeFile(file);
}

function _fillDiaryEntry(doc, date) {
  /**
   * The header looks like:
   *  _________________________
   * |       2016/08/09        |
   * |  ---------------------  |
   * |                         |
   */
  
  var title = _formatDate(date);
  var body = doc.getBody();
  
  // Title
  var titlePar = body.insertParagraph(0, title);
  var attributes = {};
  attributes[DocumentApp.Attribute.HEADING] = DocumentApp.ParagraphHeading.TITLE;
  titlePar.setAttributes(attributes);
  
  // Horizontal rule
  body.appendHorizontalRule();
  
  // First paragraph
  body.appendParagraph('\n\t');
}

function _formatDate(date) {
  var parts = [
    date.getFullYear(), 
    pad(date.getMonth() + 1, 2),
    pad(date.getDate(), 2)
  ];
  return parts.join('/');
}

function pad(n, width, z) {
  // Source: http://stackoverflow.com/a/10073788/148585
  z = z || '0';
  n = n + '';
  return n.length >= width ? n : new Array(width - n.length + 1).join(z) + n;
}