fcron has an fcrontab which you can edit.
http://fcron.free.fr/doc/en/fcrontab.5.html
https://www.systutorials.com/docs/linux/man/1-fcrontab/
The only problem with modifying the root fcrontab is that sometimes it will be overwritten with a Core Update.
Follow this post for how to create a user specific fcrontab
https://community.ipfire.org/t/my-fcrontab-file-has-been-replaced-by-a-new-one/8064/18
I have an fcrontab entry for waking up one of my servers on a regular basis. My entry is as follows:-
# Restart server at 07:30 each day
30 7 * * * /home/fcronuser/scripts/wol_server.sh
The script wol_server then has your commands etc for carrying out the wake on lan.
You might be able to put the command directly into the fcrontab line as long as it is simple. I use a script as I am also testing that the server has woken up after a period by using pings and if not then putting a message into the logs.