you can create a cron for it.
sudo apt-get update
sudo apt-get install cron
Create a bash file that will take care of the reboot:
nano /home/volumio/restart.sh
Add:
#!/bin/bash
sudo reboot
CTRL+o + CTRL+x
chmod 755 /home/volumio/restart.sh
crontab -e
Add:
0 23 * * 0 root /home/volumio/restart.sh
CTRL+o + CTRL+x