ESP is a skill that you can learn and develop. Just like any other skill, you need to learn how to perform it, and then you need to practice in order to become better at it.
So how long it takes do develop ESP depends mostly on you: People who invest an hour or so practicing every day will get results more quickly than those who practice a couple of times a week.
Our ESP training courses are about 16-18 hours. In live seminars we teach it in 2 days. In our online webinars we found that a 2-session each week for 8 weeks gave students time to practice between sessions and produced great results.
One thing that is important to remember about ESP is that it can be a 2-way street:
If you are using ESP to find out what your clients really need and what they can afford so that you can help them find what's best for them, they will sense that and will trust you.
If you are trying to find ways to persuade them to spend more so that you can get a higher commission, they will sense that too, and they want trust you.
That is why Jose Silva used to tell us that "The more you give away, the more you get to keep."
That principle is simple enough for a 6-year-old to understand: He realized that if he did a great job shining his client's shoes, they would come back to him again and again. When he added an additional service by having newspapers they could buy from his and read while he was polishing their shoes, they benefited and he earned more money.
He always kept his needs in mind. When he grew up he got married and eventually had 10 children. His attitude was that he didn't want to get the best of anybody else, but he darn sure didn't want anybody getting the best of him.
In other words: Always do what is best for everybody concerned.