It doesn't matter whether a request straddles a second or not in a throughput measuring benchmark when you saturate the system. A client would only count a request when its request call has returned. Runs it for N minutes, count up how many requests have completed, then divide the total with the time and you got req/sec.

Besides the benchmark has run for a minute. I doubt each request lasts 30 seconds.

+1.

The system is in steady state, i.e. queues of requests/responses aren't growing. Therefore it doesn't actually matter if you count the requests or the responses.