There is no guarantee with Marriott for late checkout. I can usually get 2 hours past regular checkout at non-resort properties (and I have been able to get this as a gold/platinum member). Sometimes, I will only get an hour if they have a full house the following night. I have on occasion gotten up to 3 hours extra when needed. I believe properties give late checkout priority to frequent guests at their property and higher elite members since I have heard a request for a late checkout change from a no to a yes once they saw that I was platinum/PP.

My experiences at resort properties is much more limited since I do not stay at them that much, but I have found it much harder to get a late checkout here. At the Marriott Orlando World Center, checkout is 11 am, and I had to beg for a 30 minute extension.