private static async Task OnDesiredPropertyChanged(TwinCollection desiredProperties, 
  object userContext)
{
   Console.WriteLine("desired property chPleange:");
   Console.WriteLine(JsonConvert.SerializeObject(desiredProperties));
   Console.WriteLine("Sending current time as reported property");
   TwinCollection reportedProperties = new TwinCollection
   {
       ["DateTimeLastDesiredPropertyChangeReceived"] = DateTime.Now
   };

    await Client.UpdateReportedPropertiesAsync(reportedProperties).ConfigureAwait(false);
}

protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
	_logger.LogInformation("Azure IoT Smart Edge Camera Service starting");

	try
	{
#if AZURE_IOT_HUB_CONNECTION
		_deviceClient = await AzureIoTHubConnection();
#endif
#if AZURE_IOT_HUB_DPS_CONNECTION
		_deviceClient = await AzureIoTHubDpsConnection();
#endif

#if AZURE_DEVICE_PROPERTIES
		_logger.LogTrace("ReportedPropeties upload start");

		TwinCollection reportedProperties = new TwinCollection();

		reportedProperties["OSVersion"] = Environment.OSVersion.VersionString;
		reportedProperties["MachineName"] = Environment.MachineName;
		reportedProperties["ApplicationVersion"] = Assembly.GetAssembly(typeof(Program)).GetName().Version;
		reportedProperties["ImageTimerDue"] = _applicationSettings.ImageTimerDue;
		reportedProperties["ImageTimerPeriod"] = _applicationSettings.ImageTimerPeriod;
		reportedProperties["YoloV5ModelPath"] = _applicationSettings.YoloV5ModelPath;

		reportedProperties["PredictionScoreThreshold"] = _applicationSettings.PredictionScoreThreshold;
		reportedProperties["PredictionLabelsOfInterest"] = _applicationSettings.PredictionLabelsOfInterest;
		reportedProperties["PredictionLabelsMinimum"] = _applicationSettings.PredictionLabelsMinimum;

		await _deviceClient.UpdateReportedPropertiesAsync(reportedProperties, stoppingToken);

		_logger.LogTrace("ReportedPropeties upload done");
#endif

		_logger.LogTrace("YoloV5 model setup start");
		_scorer = new YoloScorer<YoloCocoP5Model>(_applicationSettings.YoloV5ModelPath);
		_logger.LogTrace("YoloV5 model setup done");

		_ImageUpdatetimer = new Timer(ImageUpdateTimerCallback, null, _applicationSettings.ImageTimerDue, _applicationSettings.ImageTimerPeriod);

		await _deviceClient.SetMethodHandlerAsync("ImageTimerStart", ImageTimerStartHandler, null);
		await _deviceClient.SetMethodHandlerAsync("ImageTimerStop", ImageTimerStopHandler, null);
		await _deviceClient.SetMethodDefaultHandlerAsync(DefaultHandler, null);

		await _deviceClient.SetDesiredPropertyUpdateCallbackAsync(OnDesiredPropertyChangedAsync, null);

		try
		{
			await Task.Delay(Timeout.Infinite, stoppingToken);
		}
		catch (TaskCanceledException)
		{
			_logger.LogInformation("Application shutown requested");
		}
	}
	catch (Exception ex)
	{
		_logger.LogError(ex, "Application startup failure");
	}
	finally
	{
		_deviceClient?.Dispose();
	}

	_logger.LogInformation("Azure IoT Smart Edge Camera Service shutdown");
}

// Lots of other code here

private async Task OnDesiredPropertyChangedAsync(TwinCollection desiredProperties, object userContext)
{
	TwinCollection reportedProperties = new TwinCollection();

	_logger.LogInformation("OnDesiredPropertyChanged handler");

	// NB- This approach does not save the ImageTimerDue or ImageTimerPeriod, a stop/start with return to appsettings.json configuration values. If only
	// one parameter specified other is default from appsettings.json. If timer settings changed I think they won't take
	// effect until next time Timer fires.

	try
	{
		// Check to see if either of ImageTimerDue or ImageTimerPeriod has changed
		if (!desiredProperties.Contains("ImageTimerDue") && !desiredProperties.Contains("ImageTimerPeriod"))
		{
			_logger.LogInformation("OnDesiredPropertyChanged neither ImageTimerDue or ImageTimerPeriod present");
			return;
		}

		TimeSpan imageTimerDue = _applicationSettings.ImageTimerDue;

		// Check that format of ImageTimerDue valid if present
		if (desiredProperties.Contains("ImageTimerDue"))
		{
			if (TimeSpan.TryParse(desiredProperties["ImageTimerDue"].Value, out imageTimerDue))
			{
				reportedProperties["ImageTimerDue"] = imageTimerDue;
			}
			else
			{
				_logger.LogInformation("OnDesiredPropertyChanged ImageTimerDue invalid");
				return;
			}
		}

		TimeSpan imageTimerPeriod = _applicationSettings.ImageTimerPeriod;

		// Check that format of ImageTimerPeriod valid if present
		if (desiredProperties.Contains("ImageTimerPeriod"))
		{
			if (TimeSpan.TryParse(desiredProperties["ImageTimerPeriod"].Value, out imageTimerPeriod))
			{
				reportedProperties["ImageTimerPeriod"] = imageTimerPeriod;
			}
			else
			{
				_logger.LogInformation("OnDesiredPropertyChanged ImageTimerPeriod invalid");
				return;
			}
		}

		_logger.LogInformation("Desired Due:{0} Period:{1}", imageTimerDue, imageTimerPeriod);

		if (!_ImageUpdatetimer.Change(imageTimerDue, imageTimerPeriod))
		{
			_logger.LogInformation("Desired Due:{0} Period:{1} failed", imageTimerDue, imageTimerPeriod);
		}

		await _deviceClient.UpdateReportedPropertiesAsync(reportedProperties);
	}
	catch (Exception ex)
	{
		_logger.LogError(ex, "OnDesiredPropertyChangedAsync handler failed");
	}
}