Here's a study plan for you:
gmat-study-plan-start-your-gmat-journey-80727.html you can research all the study material through this post also.
I would recommend that you buy some basic quant books so that you can really drill down on the basic concepts and foundations for math. Without those foundations you will not be able to push your score higher. With a score 27 it is obvious that you are still lacking the foundations.
Books like these:
https://www.amazon.com/Ultimate-Math-Ref ... 0967759404 https://www.amazon.com/gp/product/193570 ... 1935707590 will help with the basics, and then you can start building through books like the 8
Manhattan GMAT guides (5 of them are quant related) and they will cover EVERY type of problem you can see.
How long you should take to study is totally dependent on how much you study. But I would say that if Quant is a tough subject for you, and you've already been studying, that it could take awhile to see solid improvements. But keep putting the time in and it will pay off. I would recommend also keeping an
error log so that you can work through the problems you miss and learn why you are missing them.
Good luck!