[Unit]
Description=Runs service every 3 days for %i service (00:00)

[Timer]
OnCalendar=*-*-1,3,6,9,12,15,18,21,24,27,30 00:00:00
AccuracySec=6h
RandomizedDelaySec=1h
Persistent=true
Unit=%i.service

[Install]
WantedBy=default.target