Been working on a system like this for a while now. I worked on one for a few weeks back in December, and I just started trying to solve the issue of making an animation play at a lower framerate. I've tried countless methods, none of which fully encompassing the use cases that one would use the animator component for. I finally found this, and hoped it would work (and hoped to look at the source code to figure out how you got it working). However, upon adding it to my project, none of it works. The example scene doesn't work. The script does nothing when added, because all it's doing is playing the animation at the calculated frame in update, despite the animator speed being 1, which means it basically just plays the animation like normal, regardless of the values passed into the variables. I'd love to understand why it works in the gif, but does not work when imported.
(Update: The reason it wasn't working is because, in the script, the "Play" function requests a normalized time, and this script assumes you're giving a frame-based time. Unfortunately, this method, while simpler than anything I ever did, still has the same pitfalls as my previous methods. Lowering the framerate also slows down the animation itself, which is not satisfactory or encompassing of all the use cases, unfortunately.)