What do people regard as a "sensibly low" time-out figure to hopefully ensure these "rogue" aircraft are removed ASAP from My Flights ?
Depends on whether you get these miscodes or not. I've never noticed any corrupted hex codes, but I'm in a low traffic area with patchy reception conditions, so I set local timeouts to 30/90 (30s to timout, 120s to delete). That does mean that if my RB received a corrupted hex code, it would stay on screen for 2 minutes.
It's a compromise between high timeouts to keep aircraft on screen during lost reception, and low timeouts to ensure "miscodes" dissapear quickly. In high traffic areas with good reception conditions, I would set the timeouts to less than 30/90.