Changez lived in America for four and a half years.  He spent four years at Princeton University in New Jersey.  He worked odd jobs, studied late at night, was very frugal, and cultivated a reputation for being representative of cultivated tastes, even though he was quite middle class.  During his Senior year, Changez applies for a job at the valuation consulting firm, Underwood- Samson.  From this point, Changez works at the prestigious firm.  Changez's time in America takes him just a bit after the September 11 Attacks.  His time living in America extends to the point where he is able to understand the response that America develops to the attacks as one of a nostalgic return to its World War II demeanor.  

Changez's time in America extends a little bit into this realm for at this point he is fired from his job and decides to return back to Pakistan in order to carry out his new calling as a Professor who preaches the idea that Pakistan shold be independent and not reliant on Western nations such as America.  This entire transformation is predicated upon the four and a half years Changez lived in America.