Crontab Manager will provide a new panel in the Server Manager from which cron tasks can be scheduled.
Installation for SME8 and SME9
yum install smeserver-crontab_manager --enablerepo=smecontribs signal-event post-upgrade; signal-event reboot
You can access Crontab Manager interface in the server-manager and then you can easily create/delete crons. After you have made your changes and saved the session the changes will be written to the file /etc/crontab
yum remove smeserver-crontab_manager