CmdrCupcake says with the Alchemy Viewer they plan on a 2 month release cycle. So, that would be a new version every other month.
The Alchemy Viewer developers are considering moving to Linden style viewer update, which would make the Lindens happy. They would like to see all viewers using the automatic update. It has been working for me with the SL Viewer, so this is probably a good thing.