First of all, let me thank all of us you answered. You pointed out several things I needed to consider and where my idea lacks strong enough scientific backing.

I did a little more checking and research, and although I still need to double-check, I've found a few things that not only I missed or mistaken, but were not even considered.

For example, neutron stars are extremely hot (10^12 K when first formed, I believe, I need to double-check). Even a nugget would be hot enough that it would at least wither the nearby plantlife before obliterating it on impact. Whether it would be enough to flash-heat the weather or melt part of the impact site before the actual impact, I'm not sure.

Also, neutron stars have extremely powerful magnetic effects. That is sure to have an impact on Earth and the life that lives there, even if only briefly.

Next... tidal forces.

I'm sure these would be huge, and I definitely want to thank everyone for pointing those out again. However, I'm trying to wrap my brain around the exact details of the tidal forces. It would cause a bulge in the planet that would make Io's volcanism dynamo a firecracker in comparison, that's for sure. Of course, the power of gravity making the tidals would be swiftly countered by the force of the impact, but like I said, it's all in the details.

Quick sidenote, since this was mentioned. As stories go, this would be written, not film. If it got turned into a film, great, although I don't think the general public needs to worry about not getting the danger behind this threat. Make it clear that it's a neutron nugget, not something like a carboneous asteroid, and you're good to go. Those who understand or are swift enough on the uptake would pick it up - superdense object, small, but massing on scale equal to Earth.

Chandrasekhar limit - well, if a single neutron does so after 15 minutes, I can assume (easy math here) that neutronium has a half-life of 15 minutes. Not accurate, since I'm not sure that the decay of neutronium is exactly considered radioactive, but if it is, then that's another threat. The radiation from the neutron star will be extremely deadly (although I'm sure sunburn comes from UV, so I'm not sure how to incorporate this... maybe I need to do some more research on radiation. As far as the decay goes, it just means this is a short-lived weapon, once released. Should last long enough to do the job though.

Density of neutronium - come to think of it, a teaspoon did seem a little wrong. I should have known better. Of course, at 80 meters across, it now becomes detectable, so the hidden aspect is less. Of course, if this object is "warped" or "teleported" on the sunny side of Earth, where it has to impact soon before it decays away too much of its mass (or expands too quickly), the warning would be scant.

As far as it being a planet-killer - first, I didn't say it wasn't a planet-killer, I just didn't want to lump it with the category of the other planet-killers (i.e., just another really huge rock). Second, well, I'm trying for an artistic balance. Consider it the fine art of an alien's mindset on how much damage to use to wipe out everything on Earth without destroying the actual planet. Think of these creatures as saying "overkill is so gauche", and you have an idea of what I'm trying to obtain.

So shattering is okay, melting is acceptable, but vaporization is right out.

I'll post more after I've done more research on the matter.

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"So we fix our eyes not on what is seen, but on what is unseen. For what is seen is temporary, but what is unseen is eternal."
- Paul of Tarsus