I was correct!
FWP checks all RSS feeds on activation..
I have a LOT of feeds.. Hence Timeout..
Solution is to move the RSS links to another (empty) link category, reactivate FWP and then tell FWP to use that new link category..
Sounds simple, but it's a manual job.. If I'd known where fwp stores the Link Category, I could have just changed that in the database, activated, and switched back.
Sorted!
