Hi nikhilgupta1991,
Neither finishing your exam in less than 75 minutes nor taking too long on a particular question will negatively impact your GMAT score. As far as pacing on the quant section, a good rule of thumb is to spend about 2 minutes per question. However, some questions may take you less than two minutes, and some may take you longer than that. Let me provide an example to illustrate:
6^6 is equal to which of the following?
A) 46,522
B) 46,604
C) 46,656
D) 46,688
E) 46,720
In this problem, assuming you are familiar with units digit patterns, you will quickly see that when an integer with a units digit of 6 is raised to a whole number exponent, the result is an integer that has a units digit of 6. Thus, you should have correctly answered choice C in about 10 to 15 seconds. This would give you a little padding, if needed, for working a later, more difficult problem. However, if you are not familiar with the concept of units digit patterns, you could still obtain the correct answer. The computation would probably take you close to 2 minutes or more, and you would not gain the luxury of extra time for a later problem.
Understanding that some questions can be completed in under two minutes is important so that you do not stress out when you are spending a little longer than two minutes to answer others.
One final thing I wanted address. The inner workings of the algorithm used by GMAC are not made public. Although many of us can hypothesize about the algorithm, there is no way for any of us to know EXACTLY how it works. Furthermore, focus on what you can control, such as improving your GMAT skills. After all, if you know your stuff on test day, you won’t have to worry about the intricacies of the algorithm!
If you have any further questions, feel free to reach out. Good luck!