Depends on the property, for sure, as well as the local conditions. I don't know about non-platinum success, but my ability to get a late checkout really depended on the housekeeping staff, it would seem. I've never had a problem with a 1PM or 2PM check-out and have managed 4PM and 5PM a few times (when the rooms didn't need to be turned around quickly).

Hilton properties, on the other hand, have been a real pain to get a late checkout. Despite my Diamond status and spending countless weeks in two particular properties, management figures they're doing me a really big favor by giving me an extra hour to check out. Two hours extra is almost unheard of.