Quick hint on how to add a permanent task in Qnap cron (one that will be there after reboot or update).
Login to your Qnap via ssh and edit the crontab with:
vim /etc/config/crontab
And after that just run:
crontab /etc/config/crontab /etc/init.d/crond.sh restart
And that's all. One more thing that is worth mentioning, is that you should not put your sripts in /root directory. Unless you want to do some magic with your Qnap, you will loose all the scripts after reboot. So probably the best idea is not to put your scripts in /root dir.