There's no reasonable delay. The source code needs to exist before binary distribution.

When google distribute the compiled code to me, I assume the source is already available.

If distribution means I buy a phone with compiled code, I expect the sources to be readily available.

I distribution means my phone download updated software - I expect the code to be available.

Only lasts until google pushes out gpl in favour of fuchsia or something - so they can finally run away from the community code they built the android system on. Bit until then I fully expect them to actually honor the license...