Ask the hotel. You might have better luck with the guaranteed 4 pm checkout if you don't ask them to honor all other current MR Gold benefits, such as lounge/breakfast.....or the hotel could offer you a 4 or 6 pm checkout for some reasonable additional amount of money, maybe as little as $25-50, but if there's a standard for the general public, it would be 50% of the nightly room rate for 4 pm and 100% of the rate for 6 pm, although a day rate (usually to 5 pm) could be cheaper. Some hotels in places where many flights leave late at night (Argentina, Brazil, Singapore, for example) allow 8 pm or later checkouts, while some luxury hotels do the equivalent of Your24 (IIRC Peninsula Beverly Hills, etc.).