I have never understood why my fellow Evil Overlords seem to like the digital countdown timer. Sure it is a pretty color and yeah its nice to watch the numbers get closer and closer to the end point. The drawbacks though… my goodness. Using a Self destruct device to me seems to be a admission of possible defeat in and of itself though.
Since you insist on using them though we have Evil Overlord Tip #9. Basically, it says don’t use it unless you absolutely have to. For me this means using very small ones in the skulls of my minions so I can kill them as needed, preferably using some type of sub-vocal command. The whole idea of having a large red button is completely ludicrous, I’m slightly offended it is even included in the tip. The best part though is the “Spray of bullets,” you can substitute lasers or small tactical nuclear devices if you so choose. Misdirection is always the key to every successful Overlords rise to power. The On/Off switch issue is standard in every complex under my control. We also mislabel things like “Bathroom” which can cause great fun.