Is it possible for an 80 percentille guy to get 99+ percentile in a year or two through hard work? Also, If the guy has a job which consumes more than 10 hours of his life daily, how does he make the effort to appear for exams like CAT?

Hi Debnanda
It is certainly possible to score 99 percentile irrespective of what your current percentile is.
Many people do it every year. There is a story on Quora about a guy who improved from 62 to 99.93 percentile and is currently studying in IIM-C. Thus, you just need to focus on your preparation. Regarding the job part, you will have to utilise your time well. I hope you can manage 1-2 hours on weekdays and 5-6 hours on weekends. This is enough for CAT. Hope that helps.