The regulations state that you need at least 40 hours of total time to get a private pilot Certificate, although the national average is more like 60 to 75 hours of flight time. Yes some people can do it closer to 40 hours because they may have flying experience such as a glider rating. For folks with very little aviation experience the average is 60-75 hours.
TIP: If you stop training you will generally need more flight training which will cost you more in the long run. From my experience, it is best to fly three times a week, or every other day without taking large breaks. This will allow you to retain the information from the previous flight and will provide the most bang for your buck. On the other side of the spectrum, flying every day is often too much for most people and they end up not absorbing as much.
TIP: Before you start paying for flight instruction, complete your ground work and take your written exam...(for tips on how to do this the best way click here) This way you go into your flight training with knowledge which will save you $$$ in the cockpit. In other words, you will go into your flight training with lots of knowledge that will help you grasp concepts in the cockpit much easier. It also means you can breeze through your flight training without having to stop flying for a week or two to study for the written exam.