Comment by iam-TJ

  $ systemctl cat public-inbox-watch@.timer
  # /etc/systemd/system/public-inbox-watch@.timer
  [Unit]
  Description=Periodic fetch of public mailing list

  [Timer]
  # twice a day
  OnCalendar=*-*-* 5,17:35
  RandomizedDelaySec=1h
  Persistent=true

  [Install]
  WantedBy=multi-user.target