While I've never applied this type of stuff, I have been around female ginko trees that have been treated. Made a world of difference!
My advice would be 2 treatments. As I understand the way the treatment works, it basically sterilizes the flowers which would in turn produce the fruit. Apply the first treatment when the tree really begins to flower heavily, and the second treatment should come about a week or so later, to hit the remaining flowers that have begun to bloom since the first treatment. An example, and I'm guessing here, if the first treatment would normally take care of ~70% of the fruit, then the second treatment should take care of an additional 15-20% of the fruit.
We don't have to deal with ficus like that around here, since they don't get that big. They are normally indoor house plants!
Dan