Strange behavior of std::chrono / std::this_thread::sleep_for

I have implemented the following function:

bool ResponsiveSleep(atomic<bool>& flag, const float nSeconds, const float grainSec=0.1f)
{
  auto tpUntil = chrono::steady_clock::now() + chrono::duration<float>(nSeconds);
  while (chrono::steady_clock::now() < tpUntil) {
    if (flag.load(memory_order::acquire)) {
      return true;
    }
    this_thread::sleep_for(chrono::duration<float>(grainSec));
  }
  return flag.load(memory_order::acquire);
}

And I'm calling it like this to sleep for 5 seconds:

atomic<bool> flag = false;
cout << "Start sleeping: " << double(clock()) / CLOCKS_PER_SEC << endl;
TimeUtils::ResponsiveSleep(flag, 5);
cout << "Stop sleeping: " << double(clock()) / CLOCKS_PER_SEC << endl;

However, I am getting random sleeps of 20 to 40 seconds. System: Windows 10, MSVC++ 2019 v16.5.3

Could you help to troubleshoot this? I have a guess that chrono::duration<float>(x) doesn't really expect number of seconds as x, however earlier I found examples suggesting that.