I'm a Senior Software Engineer and Team Lead at National Australia Bank. I scored 695 on the GMAT Focus Edition - 98th percentile - while working a demanding full-time job, with no coaching institute and no sabbatical. What got me there wasn't more hours. It was working out exactly where my points were leaking and attacking only that, in the study time I actually had, which was early mornings and weekends. I wrote that method up as the 16-Day GMAT Jump System: https://www.akshaygmat.com/.