Everything depends on your definition of "significant" so I certainly can't just guess at a number. More significant than any other problem humanity is facing,

Everything depends on your definition of "significant" so I certainly can't just guess at a number. More significant than any other problem humanity is facing, perhaps? If that is what you mean, my completely unscientific guess would be a decimal, then a whole lot of zeros, then a one. And I would not find it prudent to do anything to avoid that possibility that takes longer than five seconds. The steps usually recommended are much bigger than that.