Yep, that sounds exactly right to me - about 30 minutes on older hardware. That's very odd to me that you have 30 minute rust build times - as someone who works on a rust project professionally, with 10KLOC, that isn't my experience at all. If Rust gets into the kernel I would expect it to account for <1% of the code, so even if it were 100x slower to compile, which it isn't, I don't see it having an impact.