systemd

systemd unit file

An example for creating a backup of a directory

[Unit]
Description=Create backup of a dir
Wants=dir_backup.timer

[Service]
Type=oneshot
ExecStart=/bin/sh -c 'tar cvzf ~/backup/somedir_$(date -I).tar.gz ~/somedir'

[Install]
WantedBy=multi-user.target

systemd-timer

An example timer unit file

[Unit]
Description=Backup a dir at certain times
Requires=dir_backup.service

[Timer]
Unit=dir_backup.service
OnCalendar=Mon..Fri *-*-* 00:00:00

[Install]
WantedBy=timers.target

You can analyse/test the timer/calendar option of your systemd-timer unit file. This way you can check if it does what you expect

systemd-analyze calendar Mon..Fri 13:00:00