Atila from Apple on the expected performance:
> For distilled StableDiffusion 2 which requires 1 to 4 iterations instead of 50, the same M2 device should generate an image in <<1 second
With the full 50 iterations it appears to be about 30s on M1.
They have some benchmarks on the github repo: https://github.com/apple/ml-stable-diffusion
For reference, previously I was getting about <3 minutes for 50 iterations on my Macbook Air M1. I haven't yet tried Apple's implementation but it looks like a huge improvement. It might take it from "possible" to "usable".