A single candidate will do 1-2 screens (this changes over time / role), plus at least 4-5 on-site interviews. That's about 7-8 hours of meetings, minimum. Having interviewed at a number of other SF tech startups, almost all of them had about the same # of interviews.
Once you're past the screen interview, you'll almost always get all 5 interviews in the pool unless you're terrible - it's more efficient to just have the candidate come in once.
Google recommends a 1:1 ratio of prep/feedback time to interview time, so it's ~2 hrs per interview even if you're not involved in the hire / no hire discussion.
The discussion here was specifically that it was likely that background checks would start disqualifying candidates, so maybe it's better to do them up front as that's cheaper than having the interviews done first... I'd say that still makes sense, at least before the pool, if you think there's a reasonable chance they'll get punted.
Subjecting someone to 17 hours of interviews borders on the inhumane.
Plus, interviews are done iteratively; you don't run the whole process for every candidate.
Moreover, background checks are the least likely to actually disqualify candidates, so they are always done last.