Wow! It's hard to find a reliable answer on the actual time it takes to become available. This is the first I have heard it takes years. What I found from your prompted research is that it depends on your microbacterial health as to how fast it breaks down and that some brands, such as epsoma, claim that 1% is available immediately available. The Epsoma brand is 0-0-6, so probably not pure Jersey Greensand. My current batch of soil has been cooking for about 4 months so hopefully it is working some, but I'm not getting deficiencies and have gone without with success.
that all being said, in rereading your original post looking for "fast acting" source of K, I apologize that my repley was completely irrelevant! Lots of good tips here though!
Jed