I tend to do something like

{microseconds, result} = :timer.tc(fn -> do_the_request(...) end)
milliseconds = System.convert_time_unit(microseconds, :microseconds, :millisecond)

I do this

start_ms = System.monotonic_time(:milliseconds)

# do the request and receive response
    
end_ms = System.monotonic_time(:milliseconds)
diff = end_ms - start_ms

I don’t know if that would work for you (I’ve seen it being used in knutin/elli), but if all of your work is done in a single process, you can put timings into the process dictionary:

defp t(key) do
  :erlang.put({:time, key}, :os.timestamp())
end

and call it in different places inside the same process

t(:start_request)
# request something
t(:done_requesting)
t(:start_parsing_body)
# parse body
t(:done_parsing_body)

and then collect the timings at some point later (you would need to be in the same process though).

Enum.flat_map(:erlang.get(), fn
  {{:time, event} = key, time} ->
    :erlang.erase(key)
    [{event, time}]
  
  _ ->
    []
end)

which would return something like

timings = [start_request: {1518, 275996, 334820}, done_requesting: {1518, 276000, 54915}]

and you can calculate diffs with :timer.now_diff/2

start_request = timings[:start_request]
done_requesting = timings[:done_requesting]

:timer.now_diff(done_requesting, start_request)
#=> 3720095 (microseconds)

You might want to read Two frequently used system calls are ~77% slower on AWS EC2 if you are on xen. I think beam uses these calls if it is compiled with --enable-gettimeofday-as-os-system-time and erl_xcomp_clock_gettime_cpu_time set to yes, but I might be wrong.

I need this time too. I was thinking to measure it by system timer probably will do the job.

Agreed. There can be quite a bit of difference here, especially when the HTTP client pool is overloaded. The function execution time can be large, even if the response time is faster.

Hackney though has metrics. (See Metrics on https://github.com/benoitc/hackney). It seems like it is tracking request and response times among other things. Perhaps it is closer to what you want.

It supports two erlang metrics libraries, but you can write your own as long as you implement the correct contract for your module if folsom or exometer is not your cup of tea or hard to integrate into elixir (I have no idea here).