Google offers a system-wide, easily accessible dark theme in Android 10 and more and more apps are receiving updates to support it. However, there is no native schedule option to switch between light and dark mode automatically. Due to Android's open nature, though, one developer was quick to introduce an app called Automatic Dark Theme that allows you to retrofit this functionality. You just have to connect your phone to your computer and run an ADB command before you can start using it.
Automatic Dark Theme allows you to select specific times to activate and deactivate the dark theme. By default, it turns on the eye-soothing mode at 10 pm and switches back to light at 7 am, but you can adjust it to your liking.
When you first install the app, it greets you with instructions on how to give it the write-secure-settings permission that allows it to change the system-wide theme. If you haven't already, you need to unlock developer settings in order to activate USB debugging. Then, you can connect your phone to your computer and run an ADB command. After that, the app checks if it has the desired permission, and you can start using it.
Automatic Dark Theme only allows you to set fixed times to switch between modes for now, but the developer says they have an option based on sunrise and sundown in the works. You could also use Tasker to change themes automatically, though Automatic Dark Theme has some advantages: It only switches modes when the phone is locked to avoid redrawing apps while you're using them, and it keeps working even when you restart your phone. Plus, the interface is far more intuitive to use.
- XDA Developers