it looks like it might actually be equation of time(?)

Probably.
The images were ( of course [:)] ) created with SH3D/Sunflow.
Time zone is GMT + 00:00 and physical placement is Greenwich Park.



So the equation of time is responsible for the wobbly shadows...


In other 3D-programs ( like f.i. Vue eXtream – where I got my first real 3D experience) the sun is just a directional light source used to create atmospheres, so you can grab it and move it about as much as you like. Even if it's a lot more complicated in SH3D, I try to use the sunlight the same way, so I often shift the date and time to change the colour and height of the sunlight. That's why I created the sundial – to observe how both the light and the shadow directions changed with time.

Here is my sundial Project-file, so you can inspect my setup.

Cecilia