this is the size of the Schwarzschild radius, not the size of the black hole. by your definition, the black hole is a rather large object. when in reality, a black hole operates more like a point particle, ie a singularity.
i'm relatively certain it doesn't work that way, at least not for mild variations. actually, humans, especially in the ages under 30, prefer a 25 hour day. (i knew psych 105 would come in handy one day!)