There's a easier one Instead of using BTCrecover tool, you can try using FinderOuter you can download it from this link below

- https://github.com/Coding-Enthusiast/FinderOuter

About the instruction check this thread below

- https://bitcointalk.org/index.php?topic=5214021.0#post_howto

I don't know how many days it would take to recover the 3 missing words, but it should take within a day depending on your PC specs.