您可以使用在4.0中Timer创建Delay方法：

public static Task Delay(double milliseconds)
{
    var tcs = new TaskCompletionSource<bool>();
    System.Timers.Timer timer = new System.Timers.Timer();
    timer.Elapsed+=(obj, args) =>
    {
        tcs.TrySetResult(true);
    };
    timer.Interval = milliseconds;
    timer.AutoReset = false;
    timer.Start();
    return tcs.Task;
}