The basic unit for CPU time is a nanosecond. This is too small a measure to develop an intuition for. But you can build intuition by comparison. In the “Time for Computers” episode of the Two's Complement podcast, Matt Godbolt tries to tackle this by comparing the CPU time scale with a human time scale. This really helped me, so i'm reproducing a hand-wavy transcription of that scale here:
When you use Rust, it is sometimes outright preposterous how much knowledge of language, and how much of programming ingenuity and curiosity you need in order to accomplish the most trivial things. When you feel particularly desperate, you go to rust/issues and search for a solution for your problem. Suddenly, you find an issue with an explanation that it is theoretically impossible to design your API in this way, owing to some subtle language bug. The issue is Open and dated Apr 5, 2017.
I am at a point where I feel comfortable reading and writing rust code. It is a peculiar type of comfort though, verging on Stockholm syndrome. The emotional instability it causes me is baffling. One minute, I am prancing about because of a solution I was able to write using the language's constructs (ControlFlow anyone?). The next, progress seems so hopeless that I am actively considering picking up another language so I can get actual work done instead of horsing around with the borrow checker. Lifetimes take my mind hostage. The language throws wrenches into my API design. But I always come back.