I just had some success running android builds on a self-hosted github runner. One of the big setting up stages was having sdkamanger pull down large dependencies (SDK, emulator images etc.) on startup.
Forcing sdkmanager into http_only mode and pointing it at a properly-configured squid took a large percentage off the build time.
Similar story for the gradle build, where running a remote gradle cache node locally to the job means gradle steps get automatically cached without any magic CI pipeline steps.