The reason companies have that many interview hours spread across multiple slots is that then have fallout over the funnel.

They don’t have every candidate scheduled for the entire time of all the rounds. If you don’t pass earlier rounds, they’re not going to waste time (yours and theirs) hauling you through more rounds of interviews.

If you make it to the end of all of those scheduled interviews, there’s probably a very good chance you’re getting an offer.

I understand that, but it's still possible to devote up to 9 hours to this and get nothing in return. And maybe not just possible, but likely. We don't know how eagerly their pipeline rejects candidates. Every candidate has to take that gamble.

9 hours just seems excessive. Other companies have "funnel" hiring processes like this and still manage to do it in 3 hours instead of 9.