importscannerdisk.service

# /etc/systemd/system/importscannerdisk.service
[Unit]
Description=Import images from scanner SSD card
Requires=media-sauer-DOCSCAN.mount
After=media-sauer-DOCSCAN.mount

[Service]
ExecStart=/bin/true

[Install]
WantedBy=media-sauer-DOCSCAN.mount

mount scanner disk.md

Set disk label (on a built-in multimedia card reader, in my case):

sudo umount /dev/mmcblk0p1
mlabel -i /dev/mmcblk0p1 ::docscan

prompt $ mlabel -s -i /dev/mmcblk0p1
 Volume label is DOCSCAN    

Create systemd service:

sudo systemctl edit --force --full importscannerdisk
sudo systemctl enable --now importscannerdisk.service

Proof!

23:57 $ sudo journalctl -u importscannerdisk
-- Logs begin at Tue 2020-06-09 09:39:44 CDT, end at Sun 2020-09-13 23:58:15 CD>
Sep 13 23:53:38 krieger systemd[1]: Started Import images from scanner SSD card.
Sep 13 23:53:38 krieger systemd[1]: importscannerdisk.service: Succeeded.
Sep 13 23:57:47 krieger systemd[1]: Started Import images from scanner SSD card.
Sep 13 23:57:47 krieger systemd[1]: importscannerdisk.service: Succeeded.