Go to Sleep in an open-source app that basically enables you to create a countdown timer that notifies you when it's time to sleep. Of course, you'll have to enter your normal bedtime for the app to work. From the app's options menu, you can easily set your bedtime. Not only that, but you can also choose the number of notification you want to receive from the app. If you choose one, for example, you will only be notified at your actual bedtime, while if you choose multiple notifications you'll be notified a few time beforehand. Go to Sleep is an app with a simple concept that can help you improve your sleep schedule. Not only that, but the developer of this open-source app encourages all it's users to take a look at its code themselves and contribute to the project with new ideas.
Android 5.0 or higher required