This is a significant undertaking, and there is no release date or current timescale. I am one developer building Quiver from passion while continuing to improve and support the iOS app.
Registering your interest helps demonstrate the value of an Android release and informs how I prioritise it alongside continued iOS development. You can volunteer to test early versions, or simply ask to be notified when the official Android release is ready.
Volunteering does not guarantee early access. Test versions may be incomplete and will be offered only when they are ready for useful feedback.