Downloading NightOwl 0.3.2 for Mac from the developer's website was possible when we last checked. We cannot confirm if there is a free download of this app available. We recommend checking the downloaded files with any free antivirus. The program lies within System Tools, more precisely System Optimization. The actual developer of this free software for Mac is Benjamin Kramser.
From the developer:
NightOwl is a lightweight application that lets you toggle macOS Mojaves Dark Mode. The tool resides in your Mac menu bar so you can toggle between Dark and Light Mode without having to go into your System Preferences. You can set the times you want your Mac’s Light and Dark Mode to take effect. You can also have it adjust automatically at sunrise and sunset in your location.
You may want to check out more software for Mac, such as YoruFukurou, which might be related to NightOwl.