So, yes, I forgot to account for FSA earned time, of which up to 12 months can be applied to early supervised release (essentially, parole, though its not called that) and the remainder for pre-release custody (home confinement or residential re-entry center insteas of prison.) so, by completing the right activities, SBF could be on a parole-like status in ~20 instead of ~21 years, and in custody but not in actual prison in ~12.5 years.

That's not an automatic reduction (or even as close to it as good conduct time), as it requires successful participation in specified activities, but it is generally available except for a defined list of mostly violent offenses.