Time limit to serve defendant civil complaint

Yes. The California Rules of Court require you to serve the defendants within 60 days of filing, and to file a proof of service of summons within 90 days of filing. http://www.courtinfo.ca.gov/cms/rules/index.cfm?title=three&linkid=rule3_110 There isn't really a form or procedure to ask for an extension of time to serve. It will be up to the court to issue an Order to Show Cause Re Sanctions or Dismissal if you fail to comply.

In addition to the answer of Mr. Chen: you don't indicate why you have not served the defendant: can't locate, can't afford, defendant evading service. You may wish to make a motion to serve by "publication" under the correct circumstances.

In addition to the above comments (which I agree with), I note the following. The court likely will schedule a status conference or OSC re dismissal (order to show cause why the case shouldn't be dismissed for failure to diligently serve or prosecute). If you have been diligently attempting to serve and you explain your attempts to the court it is likely the court will give you a little more time to accomplish service. Keep track of what you have been doing to serve and bring proof to any court appearance. If necessary, retain a reasonably-priced private investigator or process server to locate and serve.

San Diego Superior Court has a form that you can file to advise the court of your progress and request an extension. Doing so will ensure the Court does not set an OSC and/or issue sanctions of any kind. The form is found here: http://www.sdcourt.ca.gov/pls/portal/docs/PAGE/SDCOURT/GENERALINFORMATION/FORMS/CIVILFORMS/CIV144_RE.PDF