I have been diamond for 12 years and have never been under the impression that there is a late checkout. I have been given 6 pm in hawaii once only usually 2 or 3 there(I must be there during peak times)
I have been given 2 or 3 in HK bali and BKK but otherwise in my 300 odd stays I have never been given past 1 pm
If it wass in the Tand cs I am sure I would ahve utalised it.
I actually used to book the Sheratons In HNL for the reason of the 4pm checkout
then they started implementing the NO resorts late checkout rule
usually I do book my outward flights in the middle of the day in other parets of the world though