We became pretty comfy with it in less than a month in Aug 2017. (Let's say average guy had a few years of Python and this-and-that before that, and a ~5 year CS degree before that.) Sure, there was no async/await anywhere yet, but no crossbeam-channels either. And there were a lot less friendly tutorials and there were a bit more rough edges. (Especially that we did "IoT" so cross-compiling was ... an experience.)
