I pushed the Stop button after more than an hour of scanning my Time Machine backup disk. I've found the recipe for a speedy install:
1. Turn off Time Machine.
2. Dismount the Time Machine backup disk using Disk Utility.
3. Run the FileMaker updater -- it took only 5 minutes or so.
4. Re-mount the Time Machine disk.
5. Turn on Time Machine.
Pay particular attention to step #5. A couple of months ago I turned off Time Machine while I was doing some file maintenance, and I forgot to turn it back on when I was done. I didn't discover my mistake until I'd lost a couple days of backups.