old_contents: import utils
  from models import Bookmark, BookmarkUrl
  from threading import Timer
  
  #second
  t = 7200
  
  def cronjob():
      def update_bk_image():
          bookmarks = Bookmark.objects.all()
          for bookmark in bookmarks:
              if bookmark.screen_shot:
                  break
              utils.update_bk_screen_shot_async(bookmark)
  
      update_bk_image()
      Timer(t, cronjob).start()
  
  cronjob()
  
new_contents: import utils
  from models import Bookmark, BookmarkUrl
  from threading import Timer
  
  #second
  t = 7200
  
  def cronjob():
      def update_bk_image():
          bookmarks = Bookmark.objects.all()
          for bookmark in bookmarks:
              if bookmark.screen_shot:
                  continue
              utils.update_bk_screen_shot_async(bookmark)
  
      update_bk_image()
      Timer(t, cronjob).start()
  
  cronjob()
  
subject: fix cron issue