In Calif. what are the rules regarding notice of subpoena? How much notice is required by law?

You may get this response too late since it's 2/14, but subpoenas are court orders, not invitations, and they're punishable by contempt proceedings for wilfull violations of lawful court orders, including fines and jail time. While often lawyers and DAs try to accommodate witness's scheduling requests, the lawyers are beholden to the judge's schedules are often can't allow witnesses the conveniences of appearing when they want. Your mom's birthday isn't an excuse, and neither is your work schedule, since businesses have to allow you to comply with a subpoena. As little as a day's notice is enough. But --- you do have to be personally served for your non-party appearance at trial (CCP §1985) and for your appearance and production of records at trial (CCP §1987(a)). Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.

I agree with Pamela Koslyn's response. You do have to be personally served with a subpoena in order for you to be compeled to appear. Typically, 10 days notice is required, but a subpoena could be effective with only one day's notice. (See California Code of Civil Procedure sections 1985 and 1987).