Copy the following files into /etc/systemd/system/:

restart_nightly@.service
[Unit]
Description=Restarts %i every night
 
[Service]
ExecStart=/usr/bin/systemctl restart %i.service
restart_nightly@.timer
[Unit]
Description=Restarts %i every night
 
[Timer]
OnCalendar=05:00
AccuracySec=10min
 
[Install]
WantedBy=timers.target

To use, let’s assume I want to restart nginx every night. Then do:

systemctl enable --now restart_nightly@nginx.timer

And that’s it!

To verify you can type:

systemctl list-timers

And it should report something like this:

NEXT                          LEFT                LAST                         PASSED             UNIT                         ACTIVATES
Thu 2021-03-25 05:00:00 CET   19h left            n/a                          n/a                restart_nightly@nginx.timer  restart_nightly@nginx.service