systemd service and timer for scheduled reboot.

sched-reboot.service

[Unit]
Description=Scheduled Reboot

[Service]
Type=simple
ExecStart=/usr/bin/systemctl --force reboot

sched-reboot.timer

[Unit]
Description=Reboot Scheduling.

[Timer]
OnCalendar=*-*-* 01:30:00

[Install]
WantedBy=multi-user.target

@lwbt, @Xeboc, thank you for comments. Could you please, share a complete example, which follows your remarks?

@hkoba's original example is correct. My response is in response to @lwbt's question about using reboot.target

To complete the setup, put the 2 files here:

/etc/systemd/system

And tell the init system to use them:

systemctl daemon-reload
systemctl enable sched-reboot.timer

If you want to store your custom services' files somewhere out of /etc/systemd/system to make it easier to change the reboot hour for instance, you can use:

cd /correct/path/to/your/two/files
systemctl link ./sched-reboot.service
systemctl link ./sched-reboot.timer

So there are sym links in the place of the service and timer, directing to your files stored where you want.
Then, as Xeboc said above, don't forget to run:

systemctl daemon-reload
systemctl enable sched-reboot.timer

And finally you can check that your service and timer are correctly registered with:

systemctl status sched-reboot.timer
systemctl status sched-reboot.service

You should have Triggers: ● sched-reboot.service on the timer, and TriggeredBy: ○ sched-reboot.timer on the service.

If you don't need persistence, you can use systemd-run to schedule the reboot fairly easily:

sudo systemd-run --on-calendar='2024-02-01 23:45 UTC' -- systemctl reboot --force

You also need to issue the start command to enable to timer schedule:
systemctl start sched-reboot.timer