Short answer, 10 to 15 hours. I have seen it take less than 10 hours and more than 30 hours, even with a person who was a good student and is a great pilot, and now even an instructor. There are two aspects: one is actual skill and the other is confidence. Some people get the skill, but still want the instructor in the aircraft because they don’t have full confidence in their ability yet. That situation should not be rushed, because without confidence, fear can displace skill.