Those numbers look pretty close to what I got for my 400-ton microhole. Same order of magnitude, I think.

The point isn't that it has relatively small gravity of its own, though; what brings in the goodies is the gravitational gradient, and that's immense, locally. The microhole would be a true "spacetime warp", producing incredible effects... but on a very small scale.

In my story, I started by figuring the thing would leave a one-atom-wide hole through a planet as if fell through. Unfortunately, that turned out to be negligible; the Earth would still outlive the 5 billion years (or so) the sun has left. So I worked backward from how long I wanted it to take to eat a planet, waved my hands a little, and argued that it drew in atoms from a 10-atom radius or so, and grew exponentially; I got the number down to a few thousand years -- and considerably less before the effects began to be serious (earthquakes etc.)