And is docker running via a systemd service also?
In that case, you can add an After=
line to the docker unit file, telling it to wait until after your mount service is running:
https://stackoverflow.com/questions/21830670/start-systemd-service-after-specific-service
You can use systemctl edit docker
to create an override file with this property:
https://askubuntu.com/questions/659267/how-do-i-override-or-configure-systemd-services#659268
Last suggestion: This document suggests that there may be an rclone volume plugin for docker, which could run the mount only when your specific container starts up: https://rclone.org/docker/