I haven't seen too many people who have reached the 90th percentile when starting out in the 8-25 range (for either quant or verbal). The issue there is not so much about how much time it will take but whether it will be possible at all. At the least, though, you'd be looking at 3+ months of very intensive study, likely with a private tutor.
Would it be possible to get admission in top school with that realistic score. I am Indian and heard that the average GMAT score of an Indian is high, therefore with low GMAT score it gets dicy, specially with the top 10 schools.
Are you talking about top 10 schools in the US or in India? I don't know much about the Indian schools. In the US, the top 10 schools have average scores of about 700. In order to have a good chance, it's preferable to be at or above a school's average - but those are still averages, so there are plenty of people who do get in to the top schools with sub-700 scores.
The key is: what's the rest of your application like? If every piece of your application is average, then it's going to be tough to gain admission to the most competitive schools. If there are certain pieces that are well above average, then your chances improve. Those pieces could be anything though - work experience, GPA, etc. (And I will say that admissions officers tend to advise that a very high GMAT score won't get you in. If everything about an application is average and only the GMAT is very above average, that is usually not enough.)
If you have an idea about the specific schools to which you want to apply, I'd recommend posting your question in the Ask An Admissions Consultant folder. Give them as much info as you can about your full background (undergrad institition, course of study, GPA, specific details of work experience, responsibility, promotions, specific details of extracurriculars, etc.) and, of course, mention the specific schools to which you want to apply.
In terms of your scoring goals, I would say that aiming for 90+ percentile on verbal is probably not your best plan, but that doesn't necessarily mean you can't still target 700 or high 600s - for now, at least, I would keep that goal and possibly adjust in future if it seems necessary.
If you do this, then you are going to have to get some of your improvement from quant. If you were able to raise quant from the current 45 (~75th percentile) to 49 (~90th percentile), then verbal would have to reach about 37 (around the 80th percentile - which is still going to be a challenge, but it is more realistic than 90th). If you were to score 49 on quant and 34, 35, or 36 on verbal (in the 70s), then your score would be in the high 600s.
That kind of goal would require you to get better at both quant and verbal, so you would want a course that covers both topics. Our regular courses run for 9 weeks and most students continue to study for 2 to 8 weeks after the course is over before taking the test. Because your desired score improvement is large, you would probably need at least 6 weeks and possibly longer after the end of the course, and you may also want to do some targeted tutoring for specific verbal issues (though I wouldn't think about that until after the course is over or almost over - it may not be necessary).
Obviously, the exact timing of all of this will depend upon how diligent you are with your studies. I would guess that you will need to plan for at least 4 months (possibly longer - you will need to be flexible as you see how things go) and you may also need to lower your goal from 700 (again, you will need to see how things go and adjust accordingly).