It would be counted in years, not hours. Disciplines like hand animation and anatomy are lifelong learning pursuits, and this is not an exaggeration. The good news is that these days there is practically an infinite amount of resources to learn from and many of the tools we have now make your life a lot easier.
The bad news is that the quality of work constantly raises the benchmark and you have to continuously push your own boundaries to maintain the quality level. 
This question is akin to ‘how long is a piece of string?’. There are many variables at play. Some artists can become quite decent in 1-3 years, and others might be doing it for 10 years and still be at a low level of knowledge/skill. Some artists will come into this with great 2D drawing skills, or as natural problem solvers, or with a great eye for reading and dissembling complex objects into basic forms, etc. A lot will depend on the artist. Are they naturally lazy or do they have an borderline obsession with meticulousness? There are many factors.
It’s all about the amount of quality learning time you put into it and how much passion you have for it.
I’ve been doing this stuff for 20-odd years and still have the same love and enthusiasm today, as the first year I started this. That passion always pushed me on to constantly strive to improve and to overcome the difficulties and frustrations that are an essential part of 3D.
The main thing when you’re learning, imo, is to not just be a blind button pusher, following tutorials button by button, without actually learning anything. Always question the WHY is he doing this or that, and not just what buttons are being pushed to get from A - B. Trial and error and self exploration are far more valuable learning tools than press buttons that someone is listing off to you.
Either was, the 3D learning journey never ends. The technology, techniques, methods, and tools are constantly evolving, and so should we be. On the other hand, the traditional techniques and observations that the European masters gifted us are timeless. Colour and light theory. Shadow and light. Human, animal, and cloth anatomy observations, etc. These are just as important and shouldn’t be neglected solely in favour of the technology side of things. Learning the programs and tools is the easy parts. Learning the art is the lifelong pursuit.
Best of luck. And most importantly: have fun and enjoy yourself. 