How do you suggest using GMAT Prep Verbal Question collection so that GMAT Prep Questions are not affected.
Let me put it this way........
What will you gain by saving your GMATprep right till the very end?
Either you will get a score somewhere around your expectations that will boost your confidence
OR you will get a score that will dampen your morale right before the exam.......which will do more harm than good.
I personally believe that just to get an estimation of your score before the real exam....people miss out on the opportunity to study these wonderful official questions. I would rather suggest that you give your gmatprep around 20 days before your exam....when you are done with your theory and concepts.
After which, you should focus on these official questions. These questions are the best prep material you can get. They cover almost 99% of the concepts tested on the GMAT. You do them thoroughly and I can guarantee that you will come out with flying colors.
This is just my point of view. Others may not agree. In the end, do whatever you feel is best for you.