gistfile1.txt

IEnumerator ThreeSeconds()
{
    var sw = System.Diagnostics.Stopwatch.StartNew();
    yield return new WaitForSeconds(3);
    Debug.Log(sw.Elapsed.TotalMilliseconds + "ms");
}

// 3秒でかえってくる
Time.timeScale = 1.0f;
Observable.FromCoroutine(ThreeSeconds).Subscribe();

// 6秒でかえってくる
Time.timeScale = 0.5f;
Observable.FromCoroutine(ThreeSeconds).Subscribe();