private static int SetWaitForWakeUpTime(DateTime wakeTime) {
    long waketime = wakeTime.ToFileTime();

    String timerName = "MyWakeUpTimer";
    using (SafeWaitHandle handle = CreateWaitableTimer(IntPtr.Zero, true, timerName)) {
        if (SetWaitableTimer(handle, ref waketime, 0, IntPtr.Zero, IntPtr.Zero, true)) {
            using (EventWaitHandle wh = new EventWaitHandle(false, EventResetMode.AutoReset)) {
                wh.SafeWaitHandle = handle;
                wh.WaitOne();
            }
        }
        else {
            return Marshal.GetLastWin32Error();
        }
    }
    return 0;
}

Thread t = new Thread((o) => {
        WakeData wd2 = (WakeData) o;
        try {
            DateTime now = DateTime.Now;
            DateTime next = now.Date.AddTicks(wd2.wakeTime.TimeOfDay.Ticks);
            if (next < now)
                next = next.AddDays(1);

            wd2.result = SetWaitForWakeUpTime(next);
        } catch (Exception ex) {
            wd2.ex = ex;
        }
    });
    t.IsBackground = true;
    WakeData wd = new WakeData { wakeTime = wakeTime.Value };
    t.Start(wd);

private class WakeData {
    public DateTime wakeTime;
    public int result;
    public Exception ex;
}

[DllImport("kernel32.dll")]
private static extern SafeWaitHandle CreateWaitableTimer(IntPtr lpTimerAttributes, bool bManualReset, String lpTimerName);

[DllImport("kernel32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool SetWaitableTimer(SafeWaitHandle hTimer, [In] ref long pDueTime, int lPeriod, IntPtr pfnCompletionRoutine, IntPtr lpArgToCompletionRoutine, bool fResume);