Once it’s been declassified. Executive Order 13526 specifies the necessary procedures. Among other things, it states that the original classification authority must set an expiration date, after which the information should be declassified.
If an earlier date isn’t set, documents will be automatically slated for declassification after 10 years, or a maximum of 25 years(at the discretion of the classifying authority), barring certain exceptions.
I listen to ‘I Ain’t Marching Anymore’ pretty frequently, but am not familiar with most of his catalogue. I’ll check it out!