First you need to login and view your service.
Note down your Service ID: and you Password.
http://upload.clanhost.com.au/files/1556146727.png
Have a look at this article. Choose what you want you want your schedule to do to your server. SHUTDOWN / START / REBOOT
https://www.clanhost.com.au/whmcs/index.php?rp=/knowledgebase/72/Current-list-of-Public-API-commands.html
Using the selected URL, replace the PASSWORD and SERVICE ID LINE.
http://upload.clanhost.com.au/files/1556146736.png
Now you have to register an account with https://cron-job.org/en/
You will need to create a new cron job with your URL like in this image.
http://upload.clanhost.com.au/files/1556146745.png
And thats it!