Legal Question in Criminal Law in California

No. Normally the defense attorney has arrangements with the subpoenaed witnesses to appear "on call."

You have to show up in court at the time listed on the subpoena you received. You most likely will not be allowed into the courtroom at any time, except when you are actually called to testify.

As the answer above indicates, you may make an agreement with the attorney who sent you a subpoena, promising to show up within a certain time -- usually a couple of hours -- of receiving a phone call. If you don't come to court as promised, it's the same as if you had ignored the subpoena altogether, and you could even be arrested and dragged to the courthouse.

However, "on-call" agreements are the exception to the rule. Although they are common, they are not automatic. If you have any questions, you should call the attorney who signed the subpoena.

No.