"Play before Raiders are activated. The first 4 Raiders activating in your space area automatically miss (do not roll for them)."

My confusion is regarding 'before' in the first sentence. I think it makes sense if the raiders are about to be activated by a crisis card because you know when that is coming, but what if a revealed cylon decides to activate them using location text? Can a pilot respond to that by playing Run Interference or is it too late since it says play before Raiders are activated? We allowed it in our first game, but think wording it as "Play when Raiders are activated." would have made more sense.

The raiders are actually activated when they begin following their flow chart on the back of the rulebook about who they need to attack or move to. What triggers them to activate (Crisis Cards, Cylon fleet action, By Your Command treachery card) is not the deciding factor.

In short, you were playing it right.