Why would you count that as 1 interview? It's always an exhausting 4 hour marathon of algorithms, data structures and systems design rounds with 4 different people, frequently split over a couple of days.
I've also never seen it split over multiple days. Often, pre covid, the company is flying people out and paying for hotel rooms and food at this stage and the interviewee is taking time off from their current job. An extra day adds unnecessary costs to both sides. If I was interviewing somewhere and they tried to split up this step I'd probably get annoyed and potentially cancel the interviewing process.
You could theoretically have ten 1 hour interviews, back to back in 1 day, and call it 1 step in a multistep process, but most people would call it excessive.