I was staying at the Residence Inn in London, ON and on the day of checkout I had a conference call that started at 11:30 am and ran until about 12:15 pm. After I hung up the phone I received a call from the front desk "reminding" me that I needed to check out at noon and wanting to know how much longer I'd be in the room. I asked about getting a late checkout until either 2 pm or 3 pm and was told that they didn't offer late checkouts even if the guest was a Platinum member.
This was about a year ago so I'm not sure if the policy has changed or not. At the time I was a little put off at the hotel as they gave me the impression that I was overstaying my welcome and needed to be out of the room exactly at noon. I haven't stayed at the property since but have stayed at the Fourpoints in London, ON and have never had a problem with a 4 pm checkout if needed. If the late check-out is going to be offered to Marriott Platinum guests then all of the hotels need to be made aware of the policy.