Almost every hotel asks guests to leave in the morning and arrive in the afternoon. The gap between those times is a production window, and its length is set by housekeeping arithmetic.
Rooms are serviced in series, not parallel
A housekeeper cleans one room at a time, and a full service of a vacated room takes considerably longer than the refresh given to a room whose guest is staying.
Multiply that by the number of departures and divide by the number of staff on shift, and the result is the number of hours the hotel needs between the last departure and the first arrival.
That calculation is why the standard gap sits in the middle of the day. It is long enough to turn a full house with a normal team and no longer.
Occupancy decides whether early arrival is possible
A hotel that was half empty last night has clean, unoccupied rooms available at breakfast time. Early check-in costs it nothing and is usually granted without discussion.
A hotel that sold out has no clean room until one is vacated and serviced. No amount of goodwill at the desk can produce a room that does not yet exist.
This is why the same request receives opposite answers at two hotels on the same street, and why front desk staff ask about your arrival time when you book rather than when you arrive.
The order of cleaning is a scheduling decision
Housekeeping does not work floor by floor at random. Rooms are prioritised by the arrival list, so a guest flagged as arriving early may have their room serviced first.
Requests made in advance therefore have far more effect than requests made on the doorstep. By mid-morning the sequence is already running and changing it costs more than it saves.
Room type matters too. A hotel with many identical rooms can flex easily, while one with a handful of a particular suite category may be unable to move anything at all.
Late checkout is the same problem in reverse
A room released at two in the afternoon cannot be serviced in time for a normal arrival, so a late checkout removes that room from the day's inventory.
Where the hotel is not full, the cost is negligible and the request is easy. Where it is full, granting it means an incoming guest waits.
Loyalty programmes formalise this by granting late checkout subject to availability, which is an accurate description of the constraint rather than a hedge.
Luggage storage exists because of the gap
Every hotel expects guests to arrive before their room is ready, which is why luggage rooms are standard and why staff offer them before being asked.
Some properties go further and open shower facilities or a lounge to arriving guests. These are common where long-haul arrivals land in the early morning by scheduling necessity.
Travellers arriving on those flights benefit from telling the hotel the flight number rather than a clock time, since the hotel can then plan around an arrival pattern it already knows well.