I had a tentative ruling in my California lawsuit. How long does it take the judge to view or reach his final decision?

The short answer to your question is that it depends on the judge and the type of case. In most courtrooms, however, the court will issue a tentitive ruling prior to an oral argument so that the parties and their lawyers know what judge is thinking, and to focus the oral argument. After the oral argument, the judge will usually rule with finality right then and there. Judicial departments are busy places, and judges and their staff need move on. Sometimes after oral argument, a judge will want more time to ponder the issues raised and take the matter "under submission." How long the judge takes to decided is up to the judge, but usually the ruling will be given in a week or two. On very complex cases, judges may take months to issue a ruling on a motion, but in California state courts this is rare. Everything I have written assumes your question is about California trial courts. The answer would likely be different in federal court cases, and in cases before both federal and state courts of appeal.