Function "accessWashroom" currentTime code is incomplete. Something like:

  def accessWashroom(person: String, sem: Semaphore[IO]): IO[Unit] = for {
    t0  <- IO(System.currentTimeMillis())
    _   <- IO(s"[+ 0 ms] $person wants to access the washroom, waiting for getting the access").trace
    _   <- sem.acquire
    t1  <- IO(System.currentTimeMillis())
    _   <- IO(s"[+ \({t1 - t0} ms] \)person got access to washroom and using it now").trace
    _   <- IO.sleep(5.second)
    t2  <- IO(System.currentTimeMillis())
    _   <- IO(s"[+ \({t2 - t0} ms] \)person left the washroom").trace
    _   <- sem.release
  } yield ()

does the job.