There is absolutely nothing that you can do. The jail will release him when they release him, not withstanding all of the sentencing experts in the galaxy.
If its a day late rest assured that they will justify it by some security, processing, lock-down, head-count, or other condition.
Your feelings on the matter or irrelevant and will not help him at all. If he is wrongfully detained then he can hire a civil lawyer and sue (but good luck with that).
First, second and third: No attorney-client relationship exists by virtue of any Q&A with Michael A. Haber, Esq. on Avvo. Fourth: Anything that you post on Avvo (or on similar sites) or on any social media is by its nature public. It is essentially an admission / confession and can be introduced into evidence as a statement against your interest in a subsequent legal proceeding. Once posted you lose any reasonable expectation of privacy, so, as this is an open forum (with no privilege attached), please be extra careful when considering what to post online (forewarned is forearmed.)
If he is not being released on his scheduled release date there may be a hold for him and it is unlikely that the jail would give you that information. Call his lawyer and have them get to the bottom of this.
Each case has its own facts, and we do not know any of the facts in this one. Prisoners can indeed be held beyond the anticipated release date. Gain time may not be properly awarded. The thing to do is hire a criminal defense attorney.
R. Jason de Groot, Esq., 386-337-8239