Once again there's a few discrepancies from Spice to reality. At the slowest setting we aren't quite getting down to 30 Hz.

On the fastest setting we're getting about a 50% higher frequency than expected but it looks like absolute garbage. Turning it down to ~6KHz gives us a workable waveform.

There's another weird bug that I'm not sure about. I can only bring down the output voltage to ~6V. The signal gets very degraded (Duty cycle drops and a bunch of noise appears), and below that value the 555 fails to oscillate at all. I'm not sure what the root cause of this is as the amplitude adjustment shouldn't affect the input voltage into the threshold capacitor. If anyone knows what's going on please give me a hint on how to fix this.

EDIT: Fixed! Turns out I wasn't paying enough attention and reversed a couple leads on the voltage divider. I now get the full range of 0-12V for Vmax.