Star Caribou

So the answer must be somewhere around 15.8 seconds.

The answer is about 14.8257

If you mean that there's nothing existing, including all the matter, energy, space-time, then the universe would not exist, for "universe" means "everything existing". None is none itself. And such question would be meaningless then, for no one could ever see how the universe like when everything and everyone doesn't exist. It has became quite a bothersome philosophy stuff, but once you think about it, you would get the answer. If you mean that nothing except time-space, then the answer would be quite close to your guess. "A blackhole." Actually, there's once a theory which astrophysicists like to dub it as "Theory of Nothing." It says that we could get a "child universe" by producing a blackhole. This blackhole would evaporate in 10^-34 seconds, and a merely normal blackhole when looked from the outside. But if you jump in it just in time, you would see a fast inflating universe!! Quite amazing, yet I think it would make a good guess. *"Theory fo Nothing" - mainly developed by Alan Guth and many others..