Hi Sri,
There is no 'one size fits all' answer to your question. It depends on what stage of your preparation you are at. If you've already practised RC strategies, done more than a few drills and are comfortable challenging yourself with OG RCs then by all means give yourself 2 minutes per question and no more. On the actual GMAT, no one is going to give you extra time to read the passages. But if you spend 2-3 minutes reading the passage and if you understand it well, the questions that follow can be easily answered in about 30 seconds each.
For example, yesterday I did some tough passages from OG 13e (NOT putting the question numbers so that you are not prejudiced before reaching those questions/passages.) in a little over 2 minutes per question, including reading the passage.
So you see, it's a trade off!
On the other hand, if you are more concerned with understanding and becoming familiar with GMAT RCs, you could allot yourself a few minutes (2-5) per question depending on your pace of reading and comprehension.