{time, res} = :timer.tc fn -> :timer.sleep(1000) end
# {1000575, :ok}

{time, res} = :timer.tc(fn(ms) -> :timer.sleep(ms) end, [1000])
# {1001283, :ok}

defmodule Sleepy do
  def sleep(ms) do
    :timer.sleep(ms)
  end
end

{time, res} = :timer.tc(&Sleepy.sleep/1, [1000])
# {1001106, :ok}

{time, res} = :timer.tc(Sleepy, :sleep, [1000])
# {1000352, :ok}