what will you do If you can't able to solve a quant qst in 3 mins but it is your very comfortable topic and extra 3 mins will get you to the correct answer?

Will move on, simply leave the question even if I can solve it putting 2-3 mins more it will be of no use.
consider it like this if in the start of paper i got stuck in such questions, I might miss upon few easy questions in the same time which could even give me 2-3 more easy questions. Saying from my personal experience if you stuck in a question and tried solving it despite time limit you will pay price.

if I am done with all the easy questions then definitely I will try again but only if i tried everything else

Mark for review and solve later.