The very unsatisfying answer is that nobody really knows. There aren't a lot of fossil beds immediately on either side of the K-Pg boundary, which means we don't really know how long the overall extinction took, let alone how long the recovery was, at least not on a global scale. There are estimates for the length of the extinction ranging from a few years to over 100,000.

Part of the problem is that you're dealing with an incredibly incomplete record. Preservation of fossils is rare, and finding them is difficult, so often researchers are trying to draw conclusions from very narrow sets of data and extrapolate it to the rest of the ecosystem. Like this one drawing conclusions from insect bites on fossilized leaves. They're making a lot of reasonable assumptions, but it's not exactly definitive even on a local scale.

It's also very difficult to narrow things down in geology/palaeontology to less than a few thousand years, so any numbers you find that are more precise than that aren't going to be based on actual data collected from the rocks. There's the convenient Iridium layer that generally lets you know which side of the K-Pg boundary you're on, but beyond that the most precise rock dates you can probably find would be +/-10,000 years.

So yeah. Any numbers you can get out of this are probably going to be large ranges, possibly overlapping each other.

In addition to everything else because they're basically on the ocean the water that would flood the big hole would be salty, and salt water is bad for pretty much everything. Corrodes and degrades, so you probably don't want to be spraying it all over your very expensive rockets.