For my most recent job (Staff/Principal SWE) I interviewed at four companies, each with four rounds of interviews (usual variations on 30m recruiter screen, 45m-60m tech discussion or coding exercise, 60m-90m tech deep dive, 30m-45m final wrap up with hiring manager). All over the course of about 3 weeks. It was about 16 hours in total.

No chance you can do that on "sick days", fake doctor/dentist appointments, or other such scheming. Taking many half days of personal leave just isn't workable either. You're not in full control of the scheduling to make different companies interview you one after each other on the same day, or take the same time between rounds. Some could have been scheduled in lunch breaks but not all of it.

Most people I've worked with would just schedule some "focus time" and were either WFH or headed off to a quiet part of the office or a nearby co-working space. Personal laptops are easier to use offsite obviously.