It lives in your notification shade
There is no app to keep open and nothing to find in the dark. Everything you use every night sits in one notification: the fade length with a − and + either side, the app you are listening to chosen by its icon, Pause and Restore toggles, and Start fading.
Even collapsed, the notification keeps the length steppers and Start fading on one row. While a fade runs, the same slot shows the countdown and the current volume, with +15 min and Cancel. When it ends, the panel comes back for tomorrow night.
