How long does it take you guys to complete the book?

I never went through it "end to end". I think it's important to cover the essentials up to ownership, lifetimes, generics, etc, but most of the topics after chapter 10 you can pick and choose as you come across them in real life. The most important is to just start any kind of project and see what questions you come across as you build.

Is this the book we're talking about?

https://doc.rust-lang.org/book/

It took me several months at a rather slow pace, following along with rustlings. It's definitely worth being thorough though, it has been useful knowing what I do now when I'm working on my projects. A good follow up would be building your own project, preferably something you'll use yourself.

I plowed through it like a textbook on my first read, not really to absorb it 100% but to at least make the cadence and content familiar. I read it as a reference in parts on subsequent reads.

I have never tried to read it from start to end. I went through first ~10 chapters then started to work on my projects. Then returned to some parts when needed more understanding. I noticed that some parts of the book were updated a lot during last 2 or 3 years, a lot of new information added.

I guess that varies a lot with how much programming you've done before, particularly things like functional programming and using generics.

I can't remember exactly, but I think I took about a week with fully doing the little tutorial and the customising them.

I should probably go through it again; I'm sure there's a bunch of stuff I read and forgot, or never really grokked in the first place.

And after this book, I recommend "Rust for Rustaceans" by Jon Gjenset.