If you do not want a very specific time, it might be easier to place the script in the /etc/fcron.weekly
or the /etc/fcron.monthly
directory.
Weekly → place script in /etc/fcron.weekly directory
At 02:47 on Monday. See: https://crontab.guru/#47_2_*_*_1
This is already part of fcrontab.
Monthly → place script in /etc/fcron.monthly directory
At 03:52 on 1st day of the month. See: https://crontab.guru/#52_3_1_*_*
This is already part of fcrontab.
EDIT: This should be the right command:
/sbin/shutdown -F -r now
but you will need to add it to a small script.