well, it is a very tough question to answer frankly speaking it depends upon the student itself. how much time you can devote and how long busy you remain the whole day. working personals take 12-15 months to prepare for the course. some even complete the preparation in a month. It demands that the high school mathematics and English must be above basic to have a staunch mark in the GMAT.

Basically, GMAT entitles one to a two year MBA course.

GMAT scores are accepted by a lot of elite colleges outside and inside of India

you can also check the details in the given below link about GMAT and colleges relevant to the exam

https://studyabroad.careers360.com/gmat-scores-top-business-schools-usa

all the best