# systemctl enable /path/to/this/unit-file

[Unit]
Description=Run tarsnap.service every six hours
Requires=tarsnap.service
After=network-online.target

[Timer]
Unit=tarsnap.service
OnCalendar=*-*-* 00:00:00
OnCalendar=*-*-* 06:00:00
OnCalendar=*-*-* 12:00:00
OnCalendar=*-*-* 18:00:00
RandomizedDelaySec=3m
AccuracySec=1s

[Install]
WantedBy=timers.target