It does not really matter for Avalanche, since our product does not rely on Aperture to run anymore, nor to be installed on your Mac. 

This is because Avalanche is not a plugin and works in a totally standalone manner, being able to open your Aperture libraries without any help.

So the answer is : "No, it is not too late for your Aperture libraries to be migrated, even you are already on Catalina."

Happy migration !

(*) it turns out the Aperture can still be run on Catalina with the help of a program called Retroactive. As of the time of writing, we have tested this solution and it works well to open a library. We haven't done any extensive testing or tried to use it to edit pictures. But is a reassuring to know that Aperture can still be opened in emergency if you need to. 

We still recommend to migrate existing libraries to another app of your choice that is supported by Avalanche as Aperture is not maintained anymore and its performance and stability are bound to degrade.