Oh, I think that's impossible to say how long therapy will take.

There are way too many factors involved in accurately gauging a time course.

It's a bit like predicting the course and strength of a hurricane (which is a science BTW). All we can do there is plug in all the variables that we currently know could affect the system, and hit the "enter" button on the supercomputer. Even then, the models do not always agree. It's at best a wild estimate at the beginning and an educated guess toward the end.