Legal Question in Civil Litigation in California

That depends on what it is for.

The way you have stated it is confusing. Under the California Rules of Court governing fast track civil cases, the summons and complaint are supposed to be served within 60 days of filing. Each county court system has different methods of enforcing this. Some set Orders to Show Cause or review hearings, to prompt plaintiffs to get the service accomplished.

My guess is that you mean a subpoena, not a summons. A subpoena must be served a reasonable number of days before the court date when you want the witness to appeal. What's reasonable will depend upon the circumstances. You should give the witness at least ten days if at all possible, and more if you expect him or her to bring documents or other evidence.