How to randomize particles' angular speeds about Z axis

I have a particle system dropping small flat objects from above (high along +Z axis falling toward -Z) with a camera below (Z = -100) looking up. All is working fine. But I want the falling objects to spin about Z (not any other axis). I can do that with the “Angular Velocity” setting but it makes all the particle objects rotate the same speed. I want those speeds to be random, from -0.4 to +0.4, not caring about the exact probability distribution.

I could swear I once saw a “randomize angular speed” slider or something like that once upon a time, but maybe that’s just a wish.

Perhaps there’s a way using Geometry Nodes to rotate each particle as I please using random numbers and time as inputs?