Device Inactivity - when device goes to Sleep - Android

I've been working on this for a couple of days. I have an app that needs to time out after a predefined number of minutes (have this saved in the device settings). I had tried the xamarin forms onsleep/onresume but they weren't firing at all. So I went device specific - I eventually figured out a solution for IOS by following this post - http://pranavkhandelwal.com/blog/2015/11/1/detecting-user-inactivityidle-time-for-xamarinios.

For Android - I followed the advice on this forum https://forums.xamarin.com/discussion/149583/auto-logout-after-x-minutes-due-to-idle-inactivity-in-android. But I found that it wasn't handling when the device went to sleep. I've added in an override for the OnPause method and handling it in the OnResume method - my code below.

public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
    {
        internal static MainActivity Instance { get; private set; }

        public static long DISCONNECT_TIMEOUT = 60000; // 1 min = 1 * 60 * 1000 ms
        public Handler disconnectHandler;
        public DateTime pauseDate;
        public bool deviceAsleep = false;

        protected override void OnCreate(Bundle bundle)
        {
            switch (Preferences.Get("ORIENTATION", "Both").Trim().ToUpper())
            {
                case "PORTRAIT": RequestedOrientation = ScreenOrientation.Portrait; break;
                case "LANDSCAPE": RequestedOrientation = ScreenOrientation.Landscape; break;
            }

            string timeo = Preferences.Get("TIMEOUT", "10");
            int setTimeOut;
            if (Int32.TryParse(timeo, out setTimeOut))
            {
                if (setTimeOut < 1)
                {
                    setTimeOut = 10;
                }
            }
            else
            {
                setTimeOut = 10;
            }

            DISCONNECT_TIMEOUT = setTimeOut * 60 * 1000; // 1 min = 1 * 60 * 1000 ms

            TabLayoutResource = Resource.Layout.Tabbar;
            ToolbarResource = Resource.Layout.Toolbar;

            base.Window.RequestFeature(WindowFeatures.ActionBar);
            // Name of the MainActivity theme you had there before.
            // Or you can use global::Android.Resource.Style.ThemeHoloLight
            base.SetTheme(Resource.Style.MainTheme);

            base.OnCreate(bundle);

            global::Xamarin.Forms.Forms.SetFlags("Visual_Experimental");
            global::Xamarin.Forms.Forms.Init(this, bundle);
            global::Xamarin.Forms.FormsMaterial.Init(this, bundle);

            Rg.Plugins.Popup.Popup.Init(this, bundle);

            disconnectHandler = new Handler(new MyHandlerICallback(this));

            LoadApplication(new App());

            Instance = this;
        }

        public class MyHandlerICallback : Java.Lang.Object, Handler.ICallback
        {
            private MainActivity mainActivity;

            public MyHandlerICallback(MainActivity mainActivity)
            {
                this.mainActivity = mainActivity;
            }

            public bool HandleMessage(Message msg)
            {
                //ToDo
                return true;
            }
        }

        System.Action action = () =>
        {
            // Perform any required operation on disconnect
            // Close the application
            Android.OS.Process.KillProcess(Process.MyPid());
        };

        public void resetDisconnectTimer()
        {
            disconnectHandler.RemoveCallbacks(action);
            disconnectHandler.PostDelayed(action, DISCONNECT_TIMEOUT);
        }

        public void stopDisconnectTimer()
        {
            disconnectHandler.RemoveCallbacks(action);
        }

        protected override void OnStop()
        {
            base.OnStop();
            stopDisconnectTimer();
        }

        protected override void OnPause()
        {
            base.OnPause();
            deviceAsleep = true;
            // handle screen going to sleep
            // record the date and time here
            pauseDate = DateTime.Now;
            stopDisconnectTimer(); // stop the timer while device is asleep
        }
        protected override void OnResume()
        {
            base.OnResume();
            if (deviceAsleep)
            {
                // if device was asleep
                // check the length it was asleep
                deviceAsleep = false;
                TimeSpan span = DateTime.Now.Subtract(pauseDate);
                if ((span.Minutes * 60 * 1000) >= DISCONNECT_TIMEOUT)
                {
                    // Close the application
                    Android.OS.Process.KillProcess(Process.MyPid());
                }
            }
            resetDisconnectTimer();
        }

        public override void OnUserInteraction()
        {
            resetDisconnectTimer();
        }
    }
}

I'm just wondering could I have done this better or is there any other alternative. As I said, I've been working on this for a couple of days and even though there are lot of posts on user inactivity - none of the solutions I found handles both user inactivity and device sleep. I'm not an Android or IOS developer so a lot of the posts that I found were hard to follow.

I'm working my way though XAMARIN - by no means an expert so any advice is greatly appreciated.

Thanks