having actually worked ffor Marriott years ago in various capacities, basically how HKPG works is

1) Clean any vacant /checked out room to get ready for checkin
2) Clean any special requests
3) Clean the "stayovers" last or in between waiting on the vacant rooms to clear.

So in general, there's a bunch of departures early to 10 am, then another deluge after 1pm when the late stayovers happen.

Weekends it gets even worse with the "pleasure traveler" as they all tend to arrive early and whine about needing early check in while those leaving always whine about having to be out by noon so stay late. That's why weekends you find HKPG knocking on the doors earlier hoping they are empty....we always scheduled HKPG an hour later on sat and sun since people were sleeping lateand they never had any rooms to clean until after 9 anyway.

Best advice, just ask for toom to be cleaned at special time and they will tend to honor that. Otherwise, they clean until 5 or 6 pm, and someone is going to be the last room cleaned. Rooms take genearally 20 to 30 minutes per to clean.