Hi Rainer,
You could make a cron job to restart the ntpd daemon every day at 6.00AM e.g. or any other suitable time for you.
/bin/echo "0 6 * * * /etc/init.d/ntpd restart > /tmp/ntpdrestart.log 2>&1" >> /var/spool/cron/crontabs/root
After that restart the cron daemon to pickup your change
/bin/kill $(cat /var/run/crond.pid)
/bin/busybox crond
Be aware that these changes will not survive a reboot. For a permanent cronjob in ESXi, you need to save the crontab file or recreate it after reboot. E.g. by means of editing the auto-backup.sh script to include your new crontab file to be saved. Links on how to do this could be found on several places like.... https://communities.vmware.com/thread/164134?start=150&tstart=0
Kind regards,
Arnold Veenema