it should be like 20 min on 16 vm cores (or 8 real cores). Almost instantaneously after that if the dev image mounts bazel repo and disk cache and the correspondent options are used in the bazel build command.
yes i use cpu-devel image from 2.6.0 for the build of course. I used to do it without docker but the interference is too great, i have been doing it exclusively on the docker container with mounted volumes for sources and caches now for some time.