If they have full occupancy then based on the hotel staffing of housekeepers and their union (if applicable) they may not be able to clean all the rooms in time prior to housekeeper's scheduled departure and will have to roll the cleaning of said number of room(s) to a future day.

Could they have adjusted schedules? Yes.
Will they? Depends on their scheduling and/or union agreement.


There are no "rules" for late checkout at IHG, unless you are a Diamond/Platinum Ambassador at an InterContinental or Inner Circle at Kimpton whereas both guarantee a 4PM departure. Any other brand within IHG or outside of those statuses, late checkout is "subject to availability" (meaning they can say "no"/decline request, without penalty from IHG and ownership).