Make sure you are reviewing extensively the problems that your doing. Spot errors in the wrong answer choices that appear in the OG and make sure you never repeat the mistake.
650 by studying a month is pretty good. I am not sure why did you rush into it. Take your time and analyze the OG. Thats the best advice I was given and it works.
About the time factor that you mentioned. If you are scoring Q49+ then the spare 20 minutes should not bother you. But if you are scoring less, there might be things that you missed which leaves a room for improvement.
Same goes for verbal as well.
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