That said, interviews serve both parties to some extent. You want to know if you like the company, too.
If the company is inconsiderate enough to demand a whole day of unpaid time, perhaps the culture is a bad fit to begin with.
It's common in some sectors, such as oilfield services, for example. About twelve hours with some breaks. I remember going through that with Schlumberger. The last step was getting called into an office, being asked to sit down, and told to assemble a set of mechanical pieces of some proprietary equipment you've never seen on the table. No blueprint. No context. You have five minutes. Go.
The interviewer tries to build up pressure calling the time every thirty seconds or so.
Yes, I assembled the pieces with time to spare. The only one who did in that batch, actually. Woohoo. They want to see how you handle pressure and they left that exercise when we were all tired at the end of the interview. "Jobs" on oil rigs are chaotic: everything can go wrong, hazardous material, lack of sleep, coordination with people you can't hear, company person on your case, tool strings getting stuck, gas kicks, blow ups, etc. You really need to keep cool and be deliberate under pressure and maintain a high level of attention and focus for extended periods of time.
Either in 4-5 hour-long, mostly technical sessions + lunch, or just in "meeting all your potential colleagues, the CEO, COO, etc." for 45min-1h each.