While getting a system-wide Dark Mode baked into Android 10 has been pleasant, having an automatic scheduler for the UI feature would make so much sense. If you didn’t already know, a scheduling option was available in the early betas for Android 10, but in discussions Android developers had during AMAs on reddit, it was said that there were issues with it in terms of implementation.
With that being said, it appears that the issues have been resolved and a scheduler for Dark Mode should be available in the next version of Android, which is on track to be Android 11.
Written by a Googler on the Issue Tracker site from Google, the following is noted.
The issue reported here has been fixed and it will become available in a future Android release.
Currently, anyone who wants to switch between Dark Mode and non-Dark Mode has to do so manually via a system toggle or directly inside the Display settings menu. This isn’t the worst thing ever, but still, a scheduler would be nice to have.
// XDA | Google