I've been through many companies (and many iterations of the process in each of those companies) but have never experienced a case where this takes only an hour

I've been through many companies (and many iterations of the process in each of those companies) but have never experienced a case where this takes only an hour annually. Even as an IC you're going to be spending at least half a day on your own self-review. This doesn't even include peer reviews, upward feedback, or talking about the results of this whole process with your manager. In my experience, the process also doesn't just happen a single time per year -- it's usually twice (plus 'check-ins' outside of that). I'm no fan of perf reviews but I have no idea how you could even run a process at all if you were to only give people 1 hour to do the whole thing end-to-end.