The short answer to this question is: a minimum of six months. But that answer requires a little more explanation. In order to start the divorce process in San Diego County or elsewhere in California, you must file a petition for dissolution of your marriage with the court, and then serve it on your spouse. The six month waiting period runs from the date the petition is served on your spouse, not the date the petition was filed.
Because divorce is a life-changing decision, this six month period gives you the opportunity to be sure that you really do want the divorce you've petitioned for. If you and your spouse agree on the terms of the divorce, you can use this time to reach a settlement agreement to submit to the court. The Judgment can be approved by the courtbefore the end of the six month waiting period and returned to the parties but the Judgment will indicate the date that the parties are officially "single" which is the end of the six month period. All orders in the Judgment are effective upon the parties signing the agreement and become orders of the court once the court approves the Judgment, even if that is before the six month period. If you do not reach an agreement or otherwise resolve the issues until after the six months, the date the court approves the Judgment is also the date that the parties are returned to the status of "single" persons.