Proving that the Task dispatching loop doesn't wait for thread scheduling quantum

Program.cs

using System;
using System.Diagnostics;
using System.Threading.Tasks;

class Program
{ 
    private static void Main()
    {
        MainAsync().Wait();
    }

    private static async Task MainAsync()
    {
        var sw = new Stopwatch();
        sw.Start();

        for (int i = 1; i <= 100; i++)
        {
            await PreciseTimer.Delay(1);
        }

        sw.Stop();

        Console.WriteLine(sw.ElapsedMilliseconds); // 103 ms

        sw.Restart();

        for (int i = 1; i <= 100; i++)
        {
            await Task.Delay(1);
        }

        sw.Stop();
        Console.WriteLine(sw.ElapsedMilliseconds); // 1544 ms
    }
}

Timer.cs

using System;
using System.Threading;
using System.Threading.Tasks;

// this is extremely wasteful, but that doesn't matter here
static class PreciseTimer
{
    static PreciseTimer()
    {
        var thread = new Thread(TimerMethod);
        thread.IsBackground = true;
        thread.Start();
    }

    private static object Lock = new object();
    private static DateTime? FireTime = null;
    private static Action Action = null;

    private static void TimerMethod()
    {
        while (true)
        {
            Action a = null;

            lock (Lock)
            {
                if (FireTime != null && FireTime.Value <= DateTime.Now)
                {
                    a = Action;
                    FireTime = null;
                    Action = null;
                }
            }

            if (a != null)
            {
                a();
            }
        }
    }

    public static Task Delay(int msDelay)
    {
        var time = DateTime.Now.AddMilliseconds(msDelay);
        var tcs = new TaskCompletionSource<bool>();

        lock (Lock)
        {
            if (FireTime != null)
                throw new Exception();

            FireTime = time;
            Action = () => tcs.SetResult(true);
        }

        return tcs.Task;
    }
}