Can an inmate get released before his earliest release date or can't be considered for parole until that date?

Parole is only available if the judge puts it in the Judgement and Committment Order. There are not many other ways to reduce one's sentence and get out earlier than your "out-date". There are always rumors and optimistic stories about law changes that inmates like to tell each other to keep hope alive for early release. But if you are going to do the crime, you are going to do 85% of the time.