I couldn't understand your question as it looks ambiguous to me. Hence, I am unable to guess what you are really looking for.
However, it depends on the # of concurrent users that particular operation is expected to support under real world usage conditions. Do some analysis on the operation from business perspective or get information from business people. It is all part of the core performance test activities.
WarofWords is right. It depends on your performance requirements and/ or performance objectives pertaining to the specific transaction. You would usually get different response times for the specific transaction if you vary the number of concurrent virtual users. You might want to set up different tests with different number of concurrent virtual users or set up a single test in which you ramp up (increase) the number of virtual users.
Another thing that you should be clear about is the definition of response time. Do the stakeholders understand it as the average response time, maximum response time, 90-percentile response time or something else?