But before this I used Metrics | Zincati to keep control of my system to check if the updates were installed.
And I had a schedule with Zincati to do the upgrade (if applicable) during night.
I think the key portion of what you found is in the phrasing, automatic staging of updates, which means, they are ready to install as soon as you reboot.
You can check if automatic updating is happening by looking at the service logs of the uupd service (journalctl -u uupd.service), and you can see if there is a staged update waiting by running the command rpm-ostree status. But it seems as though you’ll still need to manually reboot every so often to apply those staged updates.