Drag the slider to turn the clock forward. The minute hand goes around twelve times while the hour hand goes around once, so the minute hand catches up with the hour hand only every 65 minutes and change, not every hour. Count how many times they overlap between 12 and 12: it's 11, not 12.
The source code is at github.com/KirillOsenkov/LiveGeometry. It is written in .NET and Avalonia.