When I work on RC Passages how much time should I give

It all depends upon what strategy ur choosing and how much errors you are ready to accept.
IMO, there are three major strategies involved in RC :-
1). Read the passage thoroughly and comprehend it before you attack the questions(optional-may note down zist and important details, very short)..Time taking, very high accuracy, at times need not to refer back to passage,more time spent on passage and very less time on answering questions...time taken on short passage with three question 6-7 mins..medium to long passages(with 4 questions) 8-10 mins..affordable only if ur spending less than 1 1/2 min per question(average) in CR and SC.

2) Read first para of the passage thoroughly, understand the tone set by the passage and thereafter skim through the rest of the passage... comparatively less time taking...frequent referring back to passage required while answering the questions...be ready to compromise accuracy......recom when running out of time...

3) Read first para of the passage thoroughly, understand the tone set by the passage and thereafter read only the opening sentence of the next paras and skim the balance of the paras...in the end read the conclusion carefully and make a flow chart of the entire passage in ur mind(very quick 10- 15 secs) ( optional--may take very short notes)...less time consuming than option 1 but 30 sec to a min extra time taken than option 2....Questions asking for Tone, primary purpose and main idea can be answered right away without referring back to passage....Questions asking details are required to be referred back to passage ...Good accuracy.....on an average 2 min/Qn( including reading the passage)

one may chose the option that best fits the overall Verbal approach.
That's my 2 cents on RC.