At a minimum divorce in California takes 6 months from the date a Petition is served on the other spouse.
However, in certain cases parties reach agreements prior to the 6 month period, and in the final judgment filed with the court they indicate that the parties will become single in a future date (end of 6 month period). Upon signing the agreement, the parties are bound by the terms of that agreement. Therefore, technically a divorce case can be completed in much less than 6 months.
Other cases, various issues cause the case to not be resolved in 6 months and a case may take as long as several years to be resolved.