I'm going through the process now.
It started at 6:45am this morning and is currently at 2.62% complete... I think this will take some time. But I don't think it actually downloads/re-uploads the chunks, it just moves them.
I have 55TB in google drive BTW.
Also, as far as I can tell, the drive is unusable during the process, and there is no way of pausing the process to access the drive content. However, it will be able to resume from where it left off after a shutdown.
Having said all that, I have to say thanks to @Alex and @Christopher (Drashna) for mobilizing quickly on this, before it becomes a really serious problem. At least right now, we can migrate on our schedule, and until then there is a workaround with the default API keys.