https://docs.rs/subsecond for hotpatching general Rust code Live++ style.

Many of the UI frameworks have domain-specific hot-reloading on top of that (e.g. Dioxus can hot-reload CSS assets and RSX without resorting to binary patching) which covers the common case of wanting to quickly iterate on design details.

I've found the domain-specific stuff to be completely instant (even faster than a typical browser hot-reload). The hotpatching is typically around 0.5-2 seconds for me, but that does partially depend on project size (and of course hardware - I'm running an Apple M1 Pro).