It depends upon so many factors, its hard to say. Different hotels have different check-out times to begin with, and often what is acceptable to the hotel often depends on the number of reservations they have for that night, what time housekeeping is no longer on the floors and other factors.

IME, a couple hours past normal check-out time is usually not an issue. The LAX FS and Ren have been very accommodating to me in the past, but they often have flight crews that won't be checking in until very late and their housekeeping departments seem to work shifts, so they're already cleaning more around the clock.

Sometimes I need to do Webinars late in the afternoon and will ask to keep the room pretty late into the afternoon. IME, if I'm keeping the room past 3:00pm, most hotels either charge for a half-night or let me know they are not charging because occupancy is low that night so the room can sit uncleaned for a night.

Hope that helps.