This is just for information:
I have both Plex and Jellyfin dockers running on same physical server both pointing to the same content!
The metadata is Fully Up-To-Date under both dockers!
Assuming all scans have been recently run with NO EXTRA MEDIA added since the prev scan:-
Plex - Scan: 8 minutes
JellyFin - Scan 72 minutes.
If I add more media then similar times apply!
Now - 100% not a complaint - The end product looks gorgeous!!!