The results of my recent tests have proven that my code is working and that I can now be confident in sharing it. Here's a link to the repository.

It has all the basic code that handles running the motor, delays, watchdog timing, and sleeping. It's actually really short but a lot is happening.

If you are interested, you also may want to look into the previous commits. How I started off from the code made by the user Azeria from the Arduino forums, how I then slowly modified it to try out various optimizations, up to the cleaned-up version it is today.

There are still more features to be added to the project (e.g. A button to turn the watch on and off) so the code will definitely be changes to the code in the near future.