I think it's staff dependent in some cases:

In Marriott Cologne - first time I called, 12:30 late check-out (come on really?), then I called again later and I got it to 1pm.

Courtyard HK, first I got a 2pm late check-out when I was checking-in, despite the fact that I have a late flight that date. Then I asked the second time (another FD), I was granted 4pm check-out. The night before check-out I went down to the FD to sort out the payment (used GC so just wanted to get things sorted out), asked again and was given 6pm check-out.

Last time I stayed at the new CY in Hong Kong and my flight was 23.15 so I'd like a late check out (can't check in at the airport until 8pm). So I asked for a late check-out, she (lounge attendant) game me 4pm, and I asked for 6pm, she said anything over 4pm will need manager approval. I said, 'well I think I deserve it this time since your ventilation system let cigarette smell spread to my room and because of that I moved 3 times during my 9 nights stay' - one of them was 11pm.

Well, she called and got it approved. So we checked out at 6pm.

I also tried to ask for more because half of the time the process is like haggling in a market. I said 3pm, and I got 2pm.